LIBRARY OF CONGRESS. 



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UNITED STATES OP AMERICA. 



Efje Eural Science Series 

Edited by L. H. BAILEY 



THE SOIL 




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THE SOIL 



ITS NATURE, RELATIONS, AND FUNDAMENTAL 
PRINCIPLES OF MANAGEMENT 



BY 



F. H. KING 



PROFESSOR OF AGRICULTURAL PHYSICS IN THE 
UNIVERSITY OF WISCONSIN 




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MACMILLAN AND 


CO. 




AND LONDON 






1895 







COPYRIGHT, 1895 

By F. H. KING 



All rights reserved 



NorbJDoft IPrcgg 

J. S. Cushing & Co. — Berwick & Smith 
Norwood Mass. U.S.A. 



EDITOR'S PREFACE TO THE RURAL 
SCIENCE SERIES. 



The rural industries have taken on a new and quick- 
ened life in consequence of the recent teachings and 
applications of science. Agriculture is no longer a mere 
empiricism, not a congeries of detached experiences, but 
it rests upon an irrevocable foundation of laws. These 
fundamental laws or principles are numerous and often 
abstruse, and they are interwoven into a most complex 
fabric ; but we are now able to understand their general 
purport, and we can often trace precisely the course of 
certain minor principles in problems which, a few years 
ago, seemed to be hopelessly obscure, and which, perhaps, 
were considered to lie outside the sphere of investiga- 
tion. Agriculture has developed into a system of clear 
and correct thinking; and inasmuch as every man's 
habit of thought is determined greatly by the accuracy 
of his knowledge, it follows that the successful prosecu- 
tion of rural pursuits is largely a subjective matter. 
It is therefore fundamentally important that every rural 
occupation should be contemplated from the point of view 
of its underlying reasons. It should be approached in a 
philosophic spirit. There was an attempt in the older 



vi Editors Preface. 

agricultural literature to discuss rural matters fundamen- 
tally ; but the knowledge of the time was insufficient, and 
such writings fell into disrepute as being unpractical and 
theoretical. The revolt from this type of writing has 
given us the present rural literature, which deals mostly 
with the object, and which is too often wooden in its 
style. The time must certainly be at hand when the 
new teaching of agriculture can be put into books. 

For many years the writer has conceived of an author- 
itative series of readable monographs, which shall treat 
every rural problem in the light of the undying princi- 
ples and concepts upon which it rests. It is fit that 
such a series should be introduced by a discussion of 
the soil, from which everything ultimately derives its 
being. This initial volume is also an admirable illus- 
tration of the method of science, for the soil is no longer 
conceived to be an inert mixture, presenting only chemi- 
cal and simple physical problems, but it is a scene of 
life, and its physical attributes are so complex that no 
amount of mere empirical or objective treatment can 
ever elucidate them. If the venture should prove that 
the opening century is ready for the unrestrained appli- 
cation of science to rural life, then it is hoped that the 
Rural Science Series, under the present direction or 
another's, may ultimately cover the whole field of agri- 
culture. 

L. H. BAILEY. 

Cornell University, 

Ithaca, N.Y., June 1, 1895. 



PREFACE. 

In the preparation of the pages which follow, the 
writer has endeavored to have them bear to the reader 
a rational presentation of the fundamental principles of 
the soil as they relate to the immediately practical 
aspects of agriculture. The technicalities of the subject 
matter, and the lines of experimentation which have 
contributed the facts used, have been largely avoided, 
not because they are deemed unimportant, but in the 
hope that by so doing there might result a thirst for 
wider reading which would lead to a search for these 
matters in places where they are better presented than 
they could be here. 

No effort has been made to treat subjects in an 
exhaustive manner, the aim being simply to use so 
much of recorded facts as shall sufficiently enforce those 
principles underlying the management of soils which 
it is needful to understand in order that a rational 
practice may follow. The soil has been considered as a 
scene of life, where altered sunshine maintains an end- 
less cycle of changes, rather than as a mere chemical and 

vii 



viii Preface. 

mechanical mixture, and so far as possible the prob- 
lems have been given definiteness by treating them 
qnantitively. 

A free use has been made of all available literature, 
and credit is usually given by author's name in the text 
where the reference is made. 

Special acknowledgment is due to the United States 
Geological Survey for the use of cuts in Chapter I., and 
also to the National Geographic Society for Fig. 11. 

F. H. KING. 

University of Wisconsin, 
Madison, Wis., May, 1895. 



CONTENTS. 



*- INTRODUCTION. 

PAGE 

Sunshine and its Work. Nature of sunshine — Absorption 
and transformation of sunshine — Sunshine the motive 
power in winds, in evaporation, and in plant growth — 
The work of sunshine expressed in horse power — Move- 
ment of water in the soil and the circulation of sap influ- 
enced by sunshine — The complex character of sunshine . 3 

The Atmosphere and its Work. The weight of the at- 
mosphere — Part played in physiologic processes — Depth 
and density of the atmosphere — Its composition — Influ- 
ence of the atmosphere on the mean temperature of the 
earth — Selective power of the constituents of the atmos- 
phere — The distribution of water and plant food through 
wind currents 9 

Water and its Work. Part played in cooling the earth — 
Influence of tides upon the rate of rotation of the earth 

— Its work in corroding, dissolving, and transporting the 
materials of land areas — The part of water in the physio- 
logic processes of plant and animal life . . . .15 

Living Forms and their Work. The protective and de- 
structive effects of life on land areas — Part life has 
played in rock building and in producing mineral deposits 

— The great number and variety of life forms immediately 
important to agriculture 18 

Over and Over again. Cycles in nature — Conservation of 
energy — The circulation of the atmosphere — The mag- 
nitude and extent of water movement — Rotation of the 

materials of land areas 21 

ix 



Contents. 



y CHAPTER I. 

THE NATURE, FUNCTIONS, ORIGIN, AND WASTING OP SOILS. 

PAGE 

Nature and general composition of soil — Soil and subsoil — 
Difference between subsoils of humid and arid regions — 
Effect of lime on arid soils — The functions of soil — 
Plants without true roots — Influence of soil in the 
processes of evolution — The soil a water reservoir — 
The soil a laboratory — Origin of soils — Agencies in 
the formation of soil — Transition from rocks to soil — 
Methods of rock disintegration — The action of streams 
in soil growth — Sediments moved by streams — The 
shifting of water courses — Mechanical action of rains — 
Bad lands of Mississippi — Overplacement of soils — Gla- 
cial action in soil production — Part played by animals in 
soil formation — Formation of humus — Origin of swamp 
soils — Wind-formed soils 27 



i CHAPTER II. 

TEXTURE, COMPOSITION, AND KINDS OF SOIL. 

Mechanical analyses of soils — Importance of the size of soil 
grains in land values — Surface area of a cubic foot of 
soil — Influence of size of soil grains on the rate of solu- 
tion of plant food — Influence of texture on drainage and 
aeration — Chemical elements in soils — The composition 
of soils as shown by chemical analyses — Sandy soils 
compared with clay soils — The interpretation of chemical 
analyses of soils — Soils and subsoils contrasted — Soils 
of humid and arid regions compared — Chemical compo- 
sition and functions of humus — The nitrogen content of 
humus in arid and humid soils — The functions of certain 
chemical ingredients of soil — Kinds of soils — Relation of 
plants to different types of soils — Relation between plant 
food stored in the soil and that removed by crops — The 
" running out " of soils 70 



Contents. xi 



CHAPTER III. 

NITROGEN OF THE SOIL. 

PAGE 

Nitrogen content of soils of different regions — Nitrification in 
humus — Great importance of nitrogen, sulfur, and phos- 
phorus in plant life — The quantitive relation of the nitro- 
gen in crops compared with their ash ingredients, and 
these with the natural supplies in the soil — Forms in 
which nitrogen occurs in the soil — Distribution of nitro- 
gen in the soil — Distribution of nitrates in the soil — 
Sources of soil nitrogen — Nitrogen compounds derived 
from the air — Sulfuric acid derived from the air compared 
with crop demands — Absorption of ammonia from the air 
by soils — Free-nitrogen-fixing germs — Different varieties 
or species of germs — Symbiosis — Observations of Frank, 
Schlosing, Jr., Laurent, and Kosswitsch on soil algae — 
Processes of nitrification — Conditions which bring about 
denitrification 107 



/- CHAPTER IV. 

CAPILLARITY, SOLUTION, DIFFUSION, AND OSMOSIS. 

Illustrations of capillarity — Nature of capillarity and relation 
to surface tension — Strength of surface tension — Rise of 
liquids in capillary tubes — Capillary movement of water 
in soils — Measure of capillary work — Nature of solution 

— Solution of plant food from soil grains — Source of 
power in solution — Examples of osmosis — Measurement 
of osmotic pressure — Method of osmotic movement — 
Translocation of starch, etc. , in plants — The so-called 
selective power of plants 135 

r CHAPTER V. 

SOIL WATER. 

Functions of soil water — Amounts of water demanded by crops 

— Rainfall in most countries insufficient for the largest 



xii Contents. 

PAGE 

yields — Capacity of the soil for water — Rate of percola- 
tion from soils — Amount of soil water available to plants 

— The water table — Relation of water table to the surface 

— Wells — Contamination of well water by percolation — 
Movements of soil water — Rate of percolation through dif- 
ferent kinds of soil — Capillary movements of soil water in 
field soils — Influence of fertilizers on the rate of capillary 
movement — Barometric oscillations of the ground water 

— Temperature oscillations of the ground water . . . 154 



" CHAPTER VI. 

CONSERVATION OF SOIL MOISTURE. 

Amount of water retained by field soils — Influence of plow- 
ing land on the loss of soil water — Importance of early 
tillage — Importance of early seeding — Use of catch crops 
to diminish the loss of fertility — Danger in the use of 
catch crops — Comparative losses of water on land culti- 
vated and land not cultivated — Comparison between soil 
mulches of different depths — Mulching effect of soils of 
different kinds — Translocation of soil moisture caused by 
rains — Effects of cultivation on translocation of soil moist- 
ure — Translocation produced by firming the soil — Deep 
tillage to conserve soil moisture — More water available on 
drained lands — Flat and ridge culture — Influence of wind 
breaks and grass lands on the rate of evaporation . .184 



CHAPTER VII. 

DISTRIBUTION OF ROOTS IN THE SOIL. 

Distribution of corn roots under field conditions — Vertical 
distribution of roots — Extent of root foraging in soils — 
Influence of soil texture on symmetry of development . 207 



Contents. xiii 



CHAPTER VIII. 

SOIL TEMPERATURE. 

PAGE 

Importance of right soil temperature — Temperature at which 
vegetation becomes active — Observed soil temperatures at 
different depths — Influence of temperature on solution and 
diffusion in the soil — Influence of temperature on soil ven- 
tilation and upon osmosis — Temperatures favorable to ger- 
mination — Influence of soil temperature on nitrification — 
Conditions which influence soil temperature — Specific heat 
of water and of soils — Influence of evaporation on soil 
temperature — Temperatures on drained and undrained 
soils — Variation of temperature with kinds of soil — Vari- 
ation of temperature with direction and amount of slope — 
Influence of color on soil temperature — Influence of rolling 
and smoothing on soil temperatures — Temperature modi- 
fied by depth of cultivation — Percolation after rains modi- 
fies soil temperature — Means of hastening the rise of soil 
temperatures early in the season — Thorough tillage — 
Rolling — Tillage to diminish the diurnal range of soil 
temperature 218 



CHAPTER IX. 

RELATION OF AIR TO SOIL. 

Need of air in soil — Floating gardens and water culture — 
Saltpetre farming — Aeration of soil to prevent denitrifica- 
tion — Warington's experiments on water-logged soil — 
Soil ventilation to admit free nitrogen — Natural processes 
of soil ventilation — Blowing wells — Large ventilation of 
certain types of soils — Means of controlling soil ventila- 
tion — Elocculation increases soil ventilation — Influence of 
underdraining on soil ventilation — Aerating power of 
clover and other forms of vegetation — Soils may be too 
thoroughly ventilated — Hygroscopic moisture of soils . 239 



xiv Contents. 



CHAPTER X. 

FARM DRAINAGE. 

PAGE 

Area of swamp lands in the United States — Reclamation of 
swamp lands in Holland — Lands which may be improved 
by draining — Drainage systems in Illinois — Necessity of 
draining water-logged soils — Depth to which the water 
table should be lowered — Provision to prevent too rapid 
loss of water through tile drains — Distance between tile 
drains — The gradient of the ground-water surface — Rate 
of lowering the level of the water table — Natural sub-irri- 
gation — Value of such lands for intensive farming — Needs 
and methods of surface drainage — Celtic land beds — 
Draining basins without outlets — Example of field under- 
draining — Fall of drains — Cost of tile draining — Size of 
tile — Outlet of drains — Joining laterals with mains — 
Obstruction of tile drains by the roots of trees . . . 253 



CHAPTER XI. 

IRRIGATION. 

Encouragement for irrigating in humid climates — Results of 
sewage irrigation — Effect of irrigation on yield of corn in 
Wisconsin — Irrigation of grass lands in Europe — Devel- 
opment of irrigation in early times — Extent of irrigation 
at the present time — Amount of water used in irrigation — 
Methods of obtaining water for irrigation — Cost of irriga- 
tion — Irrigation of barren sands in Belgium . . . 268 

CHAPTER XII. 

PHYSICAL EFFECTS OF TILLAGE AND FERTILIZERS. 

Importance of good tilth — Effect of cultivation on the texture 
of the soil — Seeding to grass tends to restore texture sim- 
ilar to that of virgin soil — Change of texture by puddling 



Contents. xv 



— The formation of clods — How plowing affects tilth — 
Early tillage after rains to preserve good tilth — Subsoiling 
in humid and semiarid regions — Winter weathering to 
improve tilth — Burning and paring — Influence of fertil- 
izers of different kinds in altering the texture of soils — 
Capillary power and rate of percolation affected by fertil- 
izers — Physical action of soils in retaining certain salts — 
Influence of farmyard manure on soil moisture — Influence 
of summer fallowing on the relation of soil to water — The 
Lois-Weedon system of tillage — Summer fallowing in 
humid and semihumid climates ...... 27(3 



THE SOIL. 



INTRODUCTION. 

It was early one morning late in October after there 
had been several very severe frosts that a fox squirrel, 
either by chance or in deliberate search, passed under a 
large tree and found the ground thickly strewn with 
butternuts. All night these nuts had been falling by 
ones and by twos until now the ground was nearly cov- 
ered with them. As some other squirrel had done, one, 
or maybe, two hundred years before, so did this one take 
a nut, and hurrying off to a secluded spot, bury it in the 
soil beneath the forest mold. Why this was done, 
whether with the intention of recovering it for a future 
meal, or whether, like a deliberate forester, he planted 
it that another tree might grow, only that squirrel knew. 
It lay there in the ground undisturbed the winter 
through ; but in the spring, as with a thousand seeds of 
other kinds, its obstinate shell opened without a jar or 
sound. Water crept in, and the rich oil stored all winter 
in the thick meat rapidly changed into sugar, so that out 
of this and other materials borne along in streams of 
water which now were setting in from the soil, the tini- 
est cells began to form, some building a stem upward 

B 1 



2 The Soil 

into the sunshine and air, and others building rootlets 
downward and outward into the darkness and dampness 
of the soil. As the building, or growth, went rapidly on, 
it was not long before the materials stored in the nut and 
which induced the squirrel to carry it away, had all 
been used; but not, however, until, as a result of this 
use, there stood in the rich, dark mold a perfect little 
butternut tree with its roots brought into contact with 
the water among the soil grains and its green leaves 
spread where the throbbing pulses from the rising sun 
shall be made to pump the water and do the work of 
building a great forest tree. 

The processes of sprouting, budding, growing, and 
fruiting are marvelous ones, and the farmers, gardeners, 
and florists whose lots are cast among them have the 
grandest of opportunities for enjoyment and for intel- 
lectual and moral uplifting, as well as for pecuniary 
profit, if only they will train themselves to take advan- 
tage of them and then allow themselves the opportunity 
of doing so. 

Believing fully in the soundness of these words, the 
writer, in preparing this treatise, has aimed to present 
the most practical and fundamental facts and principles 
concerning the soil as largely as possible from the stand- 
point of the How? and the Why? and at the same time 
to pause now and then to view some of the wonderful 
adaptations of structure to physical environment which 
the long processes of evolution have finally produced. 
We can well afford to do this because the future develop- 
ment of agriculture can be made most rapid and most 
sure, not more by giving to the farmer new facts than 
by making him able to observe, interpret, and correlate 
the facts which each and every year's planting, hoeing, 



Sunshine and its Work. 3 

and harvesting must inevitably bring under his own eyes. 
The business of farming has now become so complex, 
the sciences to which it must look for direction are so 
numerous, and the needs of the world for great quantities 
of materials for cheap, wholesome food and clothing are 
growing so rapidly more urgent that the farmer of Nine- 
teen Hundred must rise upon a plane of better directed 
efforts and more economic methods. He can no longer 
do as most of us say the squirrel did, — plant without 
thought of adaptation or fitness, but simply as and 
because his father, grandfather, and great-grandfather 
did. 

SUNSHINE AND ITS WORK. 

Let us not drop at once into the soil and lose our- 
selves in the darkness of its details, but first let us look 
about and see how our field is related to the world at 
large and to the powers that energize in it. Let us begin 
with sunshine and the work it does. 

While we are yet a long way from fully comprehend- 
ing the nature of sunshine, we have learned enough to 
know that it is a sort of motion which comes to us from 
the sun, traveling through interplanetary space at the 
rate of 186,000 miles in a second of time, and on reach- 
ing us and being transformed into one or another form 
of energy, it does almost the entire work of the world. 
When the skillful man strikes a ball with a bat, he does 
it in such a manner that almost the entire motion of the 
bat passes into the ball, sending it far into the field, 
while the bat is brought as completely to rest at his side 
as if it had struck a bank of plastic clay. Now the sun- 
shine, coming to us from the sun, is as definitely a source 



4 The Soil. 

of power and is as capable of doing work, of setting 
something in motion, as is the bat when actuated by 
the powerful arms of the man. When the solar energy, 
or sunshine, falls upon the soil, the soil grains take up 
or absorb a portion of it as definitely as does the ball 
absorb the motion of the bat, the molecules making up 
the grains of soil have their velocities increased just 
as the ball had its motion as a whole augmented, and 
this increase of molecular motion in the soil grains is 
what raises its temperature. 

When the motion in the surface grains becomes so 
great that the soil is warm or hot, some of that motion 
is transmitted to the molecules of air coming in contact 
with the earth, and these, traveling faster than they did 
before, push one another farther apart, thus causing the 
air to expand and so become lighter, bulk for bulk, than 
the air which has not been so heated. Once in this con- 
dition, the lighter air is forced upward by that which is 
heavier, and wind is the result. In this wind we unfurl 
the sails of a vessel or set a windmill, when the motion of 
the wind becomes transformed into a motion of the mill. 
This mill attached to a pump drives the piston, and 
water is raised from the well. Thus it is the sunshine 
warms the soil, the soil expands the air, the air drives 
the mill, and the mill lifts the water. 

Take another case : When sunshine falls upon water, 
its surface molecules are set into such violent motion 
that the force of cohesion is overcome and the water 
changes to a gas, or evaporates. These rapidly moving 
molecules of water vapor rise quickly into the upper 
regions of the air where, as their motion slows down, 
the force of cohesion gains the ascendency again and 
they coalesce, forming clouds and finally large drops of 



Sunshine and its Work. 5 

rain, or flakes of snow, and fall back to the ocean again 
or upon the land, giving rise to soil moisture, to springs, 
rivulets, and rivers, or, where the temperature is perma- 
nently low enough, to ice-fields and glaciers, all of which, 
as we shall see, have had their part to play in the pro- 
duction of soil. 

But not all the sunshine goes directly back after 
being transformed at the surface. Some of it, in its 
altered guise, spreads downward in the soil, and after 
the snow is gone and while spring is advancing into 
summer and summer into autumn, a large amount of 
sunshine is being stored. It is stored by increasing 
the rate of motion in the soil, and in the lower atmos- 
phere by increasing its temperature. Now, in the tem- 
perate and polar zones, when the days become shorter 
than the nights, the rate of molecular motion so much 
slows down, because more altered sunshine is lost during 
the night than is received during the day, from both the 
surface air and surface soil in which plants live, that 
finally the intensity of molecular swing becomes too 
feeble to maintain longer the processes of growth, and 
plants begin to ripen, to shed their leaves, and finally, 
as the motion in the medium in which they live becomes 
too feeble, they fall asleep and winter has come. Con- 
versely, too, when the days become longer than the 
nights, when more blows of sunshine reach the soil dur- 
ing the light than can escape during the darkness, there 
finally becomes an amount of molecular hustle and bustle 
in which sleep is no longer possible, and spring, with all 
its fresh verdure and joyous music, bursts upon us. 

It is very essential that we fully grasp the important 
part which both direct and altered sunshine play in 
plant growth; for while we have no control over the 



6 The Soil. 

amount which may come to a given field, we can and do 
control the amount stored in the soil, and we also deter- 
mine the number of plants which shall stand upon the 
field to utilize the sunshine which does come to it. 

In constructing a house, it is not sufficient to have upon 
the ground stone, sand, lime, lumber, and nails, enough 
and to spare, together with the master builder who 
knows how these should be put together. In addition 
there must be a moving power, a source of energy, which 
is capable of raising these inert materials and bearing 
them to their places. So in building the butternut tree, 
it was not enough that the squirrel should plant the nut 
in a fertile soil with abundant moisture ; nor yet that 
there lived in the midst of that oily meat a master but- 
ternut builder capable of directing how the carbon, oxy- 
gen, hydrogen, nitrogen, phosphorus, and other materials 
should be compounded and brought together so that by 
no possible slip an acorn could drop from the boughs of 
the spreading tree; but, in addition, there must be a 
moving power, a source of energy, and this is the ether 
waves, born in the limitless ether ocean at the fiery sur- 
face of the sun so rapidly that more than 400 million 
millions of them arrive at each leaf every second, having 
come across 93 millions of miles in about eight minutes 
of time. It is under such hurried strokes as these that 
starch and sugar are made in the cells of plants and that 
cellulose is set in the framework of the tree. 

So powerful is the work of the sun against the cold 
ether of space that Lord Kelvin estimates it at 133 thou- 
sand horse power for each square meter at the sun's 
surface, and the working capacity of a cubic mile of sun- 
shine near the surface of the earth he places at nearly 
twenty-two horse power. Now, since the cubic miles of 



Sunshine and its Work. 7 

sunshine are arriving at the earth at the rate of 186,680 
per second, one section of land and the air resting upon 
it must receive 

186,680 x 12,050 = 2,249,494,000 ft. lbs., 

and this is equivalent to about one-seventh of a horse 
power for each square foot of surface. Not all of this 
power reaches the earth's surface, nor is all which strikes 
the surface converted into work. It is not the chemical 
work in the cells simply which is actuated by the sun- 
shine, but, as we shall see in another place, both the cir- 
culation of sap and the capillary flow of water in the soil 
are dependent upon it, in part, at least. 

There is another fact regarding sunshine which we 
need to understand. It is this : The waves which come 
to us from the sun are very complex in their character; 
indeed, it appears as if there were a very large number 
of them differing from one another chiefly in their length 
or, what amounts to the same thing, in the number which 
arrive in a given interval of time, much as we know to 
be the fact with musical tones differing in pitch. In the 
case of light there is a long series of wave lengths which 
are characterized by being able, when they fall upon the 
retina of the human eye, to produce the physiological 
effect which we designate as color of one sort or another. 
But associated with these color waves, there are many 
others to which the human eye is not sensitive, and 
these are designated as dark waves. Some of these are 
much shorter than the color waves, and are specially 
powerful in breaking down the molecular structure of 
many substances; that is, in producing chemical changes. 
Then again, on the other side of the light waves, there are 
dark ones of much longer periods of vibration, and these 



8 The Soil. 

long waves, to which we are insensible through the sense 
of sight, have a wonderful power of heating many sub- 
stances when they fall upon them, and one of these sub- 
stances in which we are specially interested in this study 
of soils, is water. When you take a large lens and let 
the bright sunshine pass through it, the glass is very 
little warmed by the passage, but if you hold paper at 
the light focus, it is quickly set on fire by the strong 
heating power of the dark or invisible rays. This has 
been proved by allowing the light to pass first through 
a solution of iodine in bisulphide of carbon, which is 
very transparent to the dark waves, but opaque to the 
light ones. When such waves are brought to a focus, 
they produce intense heating effects, and water is made 
to boil quickly under their influence. If, on the other 
hand, the light from the sun is first passed through a 
solution of alum in water, which is largely opaque to 
the dark waves, these are sifted out, and when the light 
waves by themselves are focused upon the water or 
paper, very slight heating effects are observed. 

The fact that water is opaque to the dark rays from 
the sun, — that is, absorbs them instead of transmitting 
or reflecting them unaltered, — lies at the foundation of 
the evaporation of it from ocean, lakes, and streams, and 
also from the soil and the leaves of vegetation in some 
degree. When these waves fall upon the water, they set 
its surface molecules in rapid vibration, that is, they 
heat them, and this increased speed of to-and-fro move- 
ment overcomes the force of cohesion and the molecules 
fly off, or evaporate, as we say. Were the water not 
opaque to these dark waves from the sun, neither snow 
nor ice would be rapidly melted in the spring, nor would 
there be as much evaporation from the ocean as we now 



The Atmosphere and its Work. 9 

have, and hence rains would be less frequent and the 
lands less productive. 



THE ATMOSPHERE AND ITS WORK. 

We have dwelt very briefly upon the nature of sun- 
shine and the part it plays in the work of the world. 
Let us next look at the atmosphere, for this, both in a 
broad way and in many details, has to do with our sub- 
ject, the soil. 

In the first place let us note that, light and imponder- 
able as the air seems to be, it nevertheless presses very 
heavily upon all surfaces at or near sea level — so heavily, 
indeed, that the pressure is nearly 15 pounds on each 
square inch of surface and more than a ton to the square 
foot. Each square rod of land lying near sea level sus- 
tains a load amounting to 289 tons, and each acre 46,200 
tons of air. Does it seem to you strange that, while the 
extended palm of one hand is pressed downward by a load 
of air equal in weight to that of the body, we are yet un- 
conscious of it? If this puzzles you, place your hand 
beneath the surface of a pail of water. The water does 
not seem to bear it down. Carry your hand to the 
bottom of the pail. Still you do not realize that it 
presses any harder, and yet the bottom of the pail is 
carrying a load of some 20 pounds, and this is evident 
enough to you when you hold the pail upon the hand. 
When the hand is immersed in the water, it is buoyed 
up with a pressure equal to that which bears it down, 
and the pressure which crowds it to the left equals that 
which would move it to the right and, so long as the 
pressures are equal in all directions, we are unconscious 
of them. As fish move through the waters of the stream, 



10 The Soil. 

the lake, or the ocean, unconscious of and unimpeded by 
the pressure of it, so do we travel along the bottom of 
an ocean of air; for such in reality the atmosphere is. 

In breathing, in drinking, and also in eating, we regu- 
larly, but unconsciously, utilize atmospheric pressure. 
Raising the ribs and lowering the diaphragm lifts off 
the outside air-pressure in part, and at once the air 
crowds in until the lungs are stretched and filled by it. 
To drink, we project the lips under water, shut off com- 
munication with the nostrils, using for this purpose the 
curtain called the soft palate, and then draw down the 
floor of the mouth, thus making the cavity larger; this 
removes part of the pressure from the water inside the 
lips, and at once the greater outside push upon the water 
fills the mouth and we are ready to swallow. Then, too, 
in eating, we place the morsel to be chewed between the 
teeth with the tongue ; but how is it removed when the 
work is finished? If you will watch yourself, you will 
observe that with both the lips and the passage to the 
nostrils closed, the lower jaw is dropped, which destroys 
the balance of pressure on the flexible cheeks, when the 
air on the outside immediately tucks them in between 
the teeth, and this crowds the morsel out, all so easily, 
so unconsciously, and in so brief a time that it is not 
without difficulty that we can convince ourselves of the 
real means used to do the work. 

It is the unbalancing of this same atmospheric pres- 
sure that produces the gentle breeze, and the terrible 
tornado; that lifts the water in the pump and in the 
siphon; that produces the draft in the chimney and the 
in-going and out-going currents of air which constitute 
soil-breathing or soil-ventilation, so essential to plant 
life. 



The Atmosphere and its Work. 11 

I have said that we are living at the bottom of an 
aerial ocean, and this ocean has a depth of 200 or pos- 
sibly of 500 miles, but, unlike the one of water, it grows 
so rapidly less and less dense as its upper surface is 
approached, that in rising upward from the ground 
through it one would leave behind him in the first 15 
miles all but 4.8 per cent of the entire mass; and yet 
this thin upper portion offers resistance enough to those 
stone-like bodies called meteors, traversing space, so 
that when they plunge beneath its surface, moving at 
their fearful rate, they quickly become intensely hot or 
are even converted entirely into gas by the great heat 
produced during the fall, long before the lower depths 
of the atmosphere are reached. 

Were we to separate the molecules of different kinds 
which together make up the atmosphere, we should find 
a large variety of them, but if, after doing so, we were to 
compare them, volume by volume, we should find, under 
average conditions, in every 100 cubic feet of air not far 
from 20.61 cubic feet of oxygen, 77.18 of nitrogen, 1.4 
of water vapor, .04 of carbon dioxide, and .78 cubic feet 
of a recently discovered gas, named argon, reported at 
the last meeting of the British Association by Lord 
Keighley and Professor Ramsey, as composing about one 
per cent of the nitrogen of the air. Professor Morley 
found at Hudson, Ohio, in his very critical analyses, 
made in duplicate daily and continued for six months, 
that the oxygen composed 20.949 per cent of the oxygen 
and nitrogen taken together, which would make the per 
cent of nitrogen 79.051. 

Besides the substances mentioned above as being found 
in the air, there should also be named, on account of 
their important relations to agriculture, ammonia and 



12 The Soil 

nitric acid, together with a modified and extremely active 
form of oxygen, named ozone ; and when it is stated that 
water, carbon dioxide, nitrogen, ammonia, and nitric 
acid, taken directly or indirectly from the atmosphere, 
contribute more than 97 per cent of all the materials 
which are built into the tissues of plants, we can begin 
to understand how great a part is played by the aerial 
ocean in the bottom of which we live. 

There is another extremely important office which the 
atmosphere performs, and that is to keep the earth 
warm. When the sunshine reaches the upper limits of 
our air, it enters it almost wholly unimpeded, and only 
as the last few miles of the lower depths are reached is 
there an appreciable number of its waves turned back 
into space or absorbed by the air in their passage 
through it. But when these ether waves break against 
the land and water surface of our planet, their force is 
very largely spent in setting the molecules of soil and of 
water swinging to and fro more rapidly than before, and 
this means to make them warmer. But to make it clear 
just how the air is able to save this warmth for us, 
another fact must be mentioned. It has been said that 
the ether waves coming to us from the sun set the soil 
and water molecules swinging when they strike against 
them. Now the opposite of this is the case at the sur- 
face of the sun. There the swinging molecules strike 
the ether of space, and by that very act lose so much of 
their power as speeds away to the earth in the waves 
produced. The rate of vibration of the molecules at the 
solar surface is, however, very rapid, so that the waves 
which are sent down through our atmosphere to the 
earth are very short, so short, indeed, that they seem to 
make their way among the molecules of our air without 



The Atmosphere mid its Work. 13 

disturbing them; but the to-and-fro motion which these 
waves engender in the earth molecules is very much 
slower, and hence when these in their turn start waves 
back through the ether toward the sun, as they do, these 
waves are much longer and are unable to make their way 
past the air molecules without setting them swinging; 
but this means to make the air warmer, it means to hold 
the sunshine imprisoned for the time being, but in the 
altered guise of terrestrial heat. 

How great this accumulation of heat is will be appre- 
ciated when it is stated that Professor Langley, after 
making a long and very careful experimental study of 
this property of our atmosphere, at the base and sum- 
mit of Mt. Whitney, in California, reached the con- 
clusion that, had our earth no atmosphere, its surface 
temperature, even under the equator at noon, would be 
200° C. below freezing, and this means a temperature 
of -328° F. 

With this fact before us, and remembering how slow- 
ing down the molecular motion in the tissues of plants, 
even to the rate of our winter temperatures, stops all 
plant growth, there is no difficulty in realizing how 
important this property of the atmosphere is to the life 
of both plants and animals. 

The transformed solar energy does not accumulate at 
the earth's surface indefinitely, but only until a certain 
degree of intensity is reached, and then the mean yearly 
out-go exactly balances the mean yearly in-come. Just 
how this balance is attained, one will readily understand 
if we use an illustration from another field. Suppose we 
have a tall vessel with a hole in one side near the 
bottom, and that into this vessel a stream of water is 
flowing over the top. Evidently the in-going stream 



14 The Soil. 

may be so large that, at first, more water enters over 
the top than escapes through the opening at the bottom; 
but there will come a time, if the vessel is deep enough, 
when the pressure forcing the water out becomes so 
great as to cause the quantity of water escaping to exactly 
equal that which enters, and under these conditions a 
balance is established. So it is with the out-going heat 
of our earth; its intensity increases under the resistance 
to its escape by the atmosphere until the jostle of the 
air molecules among themselves becomes so great that 
enough waves of the long sort escape into empty space 
to exactly compensate for those which are being trans- 
formed at and near the surface of the earth. 

Not all portions or constituents of our atmosphere 
exert the same screening power over the long dark waves 
radiated back into space by the earth. It is the lower 
layers of the air, and especially those portions which 
are heavily dust and moisture laden which exert this 
power in a pre-eminent degree. And it is because of this 
fact that soil temperatures decrease as the altitudes on 
mountain sides increase until, even under the equator, 
permanently frozen ground and eternal snow-fields and 
glaciers may be met only four or five miles above sea 
level. So, too, when the sky clears after a winter storm 
and the air has been swept exceptionally clean of its 
moisture and particles of dust by the forming crystals of 
snow, each of which has its beginning about a particle 
of dust, that the radiations escape rapidly through the 
clear air, giving rise to the cold waves which traverse 
the country in the rear of winter storms. This is also 
the reason, in part, why killing frosts in fall and spring 
usually occur only on clear nights ; and why it is that 
the temperature of arid regions falls so rapidly as soon 
as the sun has set. 



Water mid its Work. 15 

Looking at the atmosphere once more in its relation 
to life, we find that it performs a very large and very 
important work as a distributing agent or means of 
transporting the food and waste of every living being. 
Taking np the carbon dioxide as it is thrown off in the 
soil by the germs which consume dead organic matter 
there, from the lungs and tissues of animals living both 
upon the land and in the water, from the craters of 
active volcanoes, and from the fires kindled by man, it is 
borne by the winds into contact with the green parts of 
plants, where its carbon is appropriated in the processes 
of growth. Taking up the oxygen, too, as it is set free 
from the carbon dioxide in the tissues of plants, the 
winds bear it back to the soil, to the tissues of animals, 
and to the fires of the home and the workshop. Taking 
up the water, too, of which the plant must use from 200 
to 300 pounds for every pound of dry matter produced, 
it is borne fresh and sweet from the salt sea and de- 
posited upon the land, into which it sinks, to be drunk by 
the roots of plants or brought back by gravity, in the 
form of springs, to quench the thirst of animals. 

WATER AND ITS WORK. 

Water is another agent which plays an extremely im- 
portant part in the processes going on in the soil, and it 
will be helpful to us if, before entering upon details, we 
can get a broad view of the work it has done and is now 
doing. 

Studies, both in astronomy and in geology, point to a 
stage early in the history of the earth when the temper- 
ature of the solid land was very far above even a red 
heat. This being true, there must have been a time 



16 The Soil. 

when the great ocean sheets which now cover three- 
fourths of our globe to a mean depth of 16,000 feet did 
not exist as such, their waters then floating in the form of 
vapor, shrouding the whole earth in an atmosphere of 
great density. At this stage water began its great work 
which to-day is still in progress. Let us see what it has 
been. 

If the small amount of water vapor and dust particles 
existing to-day in our atmosphere play so important a 
part in holding back the dark radiations from the earth's 
surface and thus keeping it warm, as we have seen, how 
extremely opaque in those early days the atmosphere 
must have been to these long waves, and how slowly 
must the surplus heat have passed away by this method! 
And yet the first great work that water did was to greatly 
hasten the cooling of the earth down to the temperature 
at which it might become the abode of life. The man- 
ner in which it did its work was this : The water in the 
upper, clearer portions of the atmosphere lost its heat 
by radiation and, condensing into drops, fell as rain to a 
lower and much warmer level, where, at the expense of 
the heat of the region into which it had fallen, it was 
quickly evaporated, but only to rise once more into the 
upper regions to send off into space the large amount of 
heat which had been imparted to it. The vapor of water, 
being much lighter than air, rose more quickly than 
heated air currents could have done, and then, on being 
condensed into liquid drops, returned again far swifter 
than it had risen, so that the number of journeys made 
by these water molecules in their mission of cooling the 
earth far outnumbered those made by the molecules of 
oxygen, nitrogen, or carbon dioxide during equal intervals 
of time. Nor is this all, for each pound of water carried 



Water and its Work. 17 

with it on every journey many times the amount of heat 
which an equivalent amount of air was able to bear. 

The next great work that water did was to slow down 
the rate of rotation of the earth upon its axis until, 
according to the investigations of G. H. Darwin, our day 
was changed from one perhaps not longer than three 
hours to its present twenty-four. It is through the in- 
strumentality of the tides, which, acting as a friction 
brake upon the earth, .have steadily slowed its motion 
down, but much more rapidly in the early days than at 
the present time ; for then, on account of the moon being 
nearer to the earth, the tides had perhaps thirty-six 
times their present magnitude. 

As soon as large land areas emerged from the sea, then 
the third great work of water began ; a work which, 
through all this long time, has consisted in dissolving 
out, in altering, in breaking into smaller fragments, in 
grinding, and finally in transporting from higher to lower 
levels the soil, the minerals, and the rocks of all lands. 

This third work of water has been a vast one indeed, 
but just how great our present knowledge does not make 
it possible to form even an approximate estimate ; that 
it has been very large, every considerable land area bears 
ample and indisputable evidence. Take the state of 
Wisconsin as an illustration : Leaving out of the count 
the vast depth of deposits which together have been 
grouped as Laurentian, in this state we have, lying above 
them, a measured thickness of rock fragments exceeding 
30,000 feet, built from materials taken from the soils, the 
coast lines, the banks of streams, and the subterranean 
waterways of earlier land areas by this never-ceasing 
action of water. But great as has been the work of 
water here in .sweeping the dust and litter of land 
c 



18 The Soil. 

sculpturing into the sea, the strata referred to are the 
accumulations of less than half the years since the work 
began. 

Finally, with the advent of living forms upon our 
planet, water took up still another very important work ; 
for to both plants and animals it is indispensable. Mak- 
ing up the larger part of their weight, it is the medium 
in which the chemical transformations essential to the 
processes of growth take place, if, indeed, it does not play 
the part of an active and indispensable agent in bringing 
these changes about. Then, too, water not only takes up 
and holds in the liquid form those substances in the soil 
which may become the food of plants, but it is the 
medium of transportation by which all materials are 
moved from root to leaf and from the leaf back to the 
various places where the processes of growth are taking 
place. In the physiological processes of the animal body, 
it has a similar and equally important role to play ; for 
here, too, it becomes first a solvent and then a medium 
of transportation by which all food is taken to, and the 
wastes removed from, the various organs of the body. 
Finally, both in plants and animals, water acts as a tem- 
perature regulator, tending, by its evaporation from the 
surface, to prevent the tissues becoming too warm, and 
among many animals this action is very marked ; for they 
have the power, when the body is getting too warm, of 
sweating or pouring water upon the surface, where it may 
evaporate quickly and thus cool the body. 

LIVING FORMS AND THEIR WORK. 

Not only are the various forms of terrestrial life greatly 
dependent upon the soil for their well-being, but the soil 



Living Forms and their Work. 19 

itself throughout geologic time has been wrought upon in 
many and very important ways, so that a general state- 
ment of the work living forms have accomplished and 
are now doing will be a helpful preliminary to our study 
of the soil. 

All are familiar with the very rapid washing away of 
soil by the heavy rains which fall upon steep and naked 
hillsides, and also with the equally marked protecting 
influence exerted in the prevention of such washing by 
the roots and close-lying herbage of plants of almost all 
kinds. By this action land plants hold in check, in an 
extremely important manner, the destructive power of 
water and of wind, giving much deeper and far more 
fertile soils than would otherwise be possible. 

On the other hand, however, these same roots hasten 
the destruction of rocks by growing into their fissures 
and wedging them apart, and also by corroding and 
dissolving away the surfaces both of rocks and of soil 
grains wherever they may come in contact with them. 
Nor is this all, for living in the soil, chiefly in the sur- 
face 14 inches, are great numbers of microscopic forms, 
which, feeding upon the dead tissues of plants and ani- 
mals, evolve large quantities of carbon dioxide, nitric 
and other acids, which in their turn become corrosive 
agents, bearing off in the water which runs to the sea 
vast quantities of soil in solution. Mr. T. M. Eead has 
estimated that the Mississippi alone carries annually to 
the sea 150,000,000 tons of dissolved rock materials, 
while other streams bear away proportionately large 
amounts. 

But in this world of never-ending change life has done 
more than to protect the steep hillsides and to hasten the 
solution of soil and the crumbling of rocks. In addition 



20 The Soil. 

it has been a great rock-builder and gatherer of mineral 
wealth. Taking out of the sea-water the lime which the 
carbonic acid has dissolved and floated to the ocean, the 
great army of shell bearers and coral builders have, in 
all the geologic ages, laid down their mantles and frame- 
works to become the limestones of the world. In favored 
situations, too, the decay of the organic tissues of plants 
and of animals has resulted in the formation of gases, 
which, rising through the water, have precipitated from 
it iron and possibly lead, zinc, and copper as it was being 
borne along in the slow coastal currents, thus bringing 
into rich deposits in a few places these metals so indis- 
pensable to the civilization of to-day. Then there are 
our great beds of coal and peat, our deposits of asphalt 
and bitumen, and our reservoirs of mineral oil and 
natural gas, all of which are believed to have resulted 
chiefly from the decomposition of the tissues of living 
forms. 

. Truly, life, working in the laboratories of the lower- 
most layers of the atmosphere, in the surface few 
inches of the dark soil and more widely spread in the 
transparent ocean waters, using direct and altered sun- 
shine as its moving power, has done and is still doing a 
very great work. And let the farmer never forget that 
his life work is thrown among not a few cultivated plants 
and domestic animals, but rather that every farm is in- 
habited literally by thousands of kinds and millions of 
individuals, most of them microscopic, it is true, but 
powerful in their great numbers. Nor can we for a 
moment think that only those forms which we con- 
sciously aim to raise hold vital relations with us; for 
year by year, as the horizon of our knowledge of the life 
histories of the living forms about us is made broader, it 



Over and Over Again. 21 

is only yet again and again that we learn of new and 
important relations existing between them and us. 

OVER AND OVER AGAIN. 

The tide comes and goes and comes again. The morn- 
ing dawns, the sun sets, the stars come out, and once 
more the sun is in the east. The cold winds cease to 
blow, the birds come and then are gone, the snows drift 
high along the fences, but spring is sure to follow. This 
method of cycles in the ongoings of nature is so general 
and so fundamental to the constancy of results, especially 
in agriculture, that we may well pause for a brief general 
consideration of it. 

The critical and quantitive methods of investigation 
which so strongly characterize the nineteenth century 
have led us to know that neither the material of things 
nor the power which does work can be destroyed. No 
discovery of modern science is more fundamental and 
far-reaching than that of the indestructibility of both 
matter and energy, and equally fundamental is the other 
fact that, do what we will, we can create neither the one 
nor the other. 

We may, if we choose, conspire to have the energy of 
burning straw, in the fire box of the engine, converted 
into the energy of steam and transmit this through the 
piston and driving belt to the thresher where the work is 
done ; but while this is going on, through the friction of 
belts and bearings, and that of the agitation of the straw, 
grain, and air, there reappears ultimately, in the form of 
heat, an amount of energy equal to that given to the steam 
which drove the piston while doing the work, and this 
too is a measure of the direct and altered sunshine 



22 The Soil. 

required to perform the labor of building the straw used 
for fuel. Over and over again is energy used to do the 
work of the world, but in altered form and in divers 
places, nowhere destroyed and nowhere created. 

The few bushels of ashes left after burning the win- 
ter's supply of wood seem to point to a destruction of 
matter, but their weight, added to that of the products 
which escape through the chimney, is actually much 
greater than the original weight of the fuel ; for much 
oxygen from the air has united with it. So it is 
with our domestic animals ; what we realize in their 
increase of live weight, and in the weight of the dung 
and urine, falls so far short of that of the food con- 
sumed that here is a seeming destruction of matter, but 
when the materials which are thrown off in the invisible 
form from the lungs and from the skin are taken into 
the count, the wastes exceed the food consumed by the 
amount of oxygen which the animal has taken from the 
air. Now, in both of these cases, the oxygen which 
the sunshine released from the carbon in the tissues of 
the growing plant finally returns to reclaim its carbon 
again and bear it back as carbon dioxide to the atmos- 
phere from which it was taken. 

The water, too, falling as rain upon the soil, and rising 
in the sap to contribute its constituents to the building 
of the woody fibre of the fuel, or the starch and sugar 
of the food, is again returned to the atmosphere to make 
the rounds once more. It is the same way with the 
nitrogen and with the ash ingredients, — each and all 
are used over and over again, but nowhere in the round 
is there any loss of matter or any gain. 

Take our atmosphere as a whole : In the equatorial 
zone of strongest heat the air is steadily rising to a con- 



Over and Over Again. 23 

siderable height, where two currents part and move 
toward the poles, but only to return as under currents and 
to make the trip over again. Then, besides this world- 
wide circulation in the atmosphere, there is a tendency, 
most of the time, for the air to travel from the land to 
the sea and from the sea back to the land again, the 
currents being along the land surface from the sea during 
the warm portions of the year, but back again toward the 
sea overhead; then when the seasons are cold and the 
sea is warmest, the air from the land areas slides along 
their surfaces, out upon the sea, while, as an upper 
current, it travels back again to return once more ; and 
by these two great systems of winds the land is watered 
by the moisture brought from the sea, and the general 
composition of the whole atmosphere is maintained 
remarkably constant. 

In addition to these larger systems of circulation, the 
greater absorption and transformation of sunshine at 
the surface of the earth than takes place higher up in 
the atmosphere, maintains everywhere and at all times 
local ascending and descending currents, so that, no 
matter how rapidly vegetation may consume the carbon 
dioxide of the air, and put in its place free oxygen, or 
how rapidly animal life in the air, or microbe life in the 
soil, may use the free oxygen and put in its place carbon 
dioxide, these local ascending and descending currents 
keep the air so thoroughly stirred that the most care- 
ful chemical analyses reveal only exceedingly small 
variations in the relative proportions of the oxygen, 
nitrogen, and carbon dioxide in the air ; and since both 
plants and animals tend constantly to disturb this rela- 
tive proportion of gases, it is plain that by this over 
and over again process, a healthful atmosphere, so 



24 The Soil 

essential to the well-being of both plants and animals, 
is maintained. 

Let us now try to gain an idea of the magnitude of the 
movement in the endless round which water makes as it 
journeys from the sea to the land, and back from the 
land to the sea again. Observe the face of your watch 
just one minute, and then reflect that, on the average, 
during each such interval of time, the Mississippi River 
empties into the Gulf of Mexico 40 acres of water 
more than 21 feet deep; while in South America, its 
great Amazon unloads a burden nearly five times as 
large, or more than 103 40-acre-feet per minute. But 
large as this work really is, it does not measure the 
volume of water which, on the average, is steadily rising 
from the earth's surface into the atmosphere under the 
impulse of altered sunshine ; for a large part of the 
water which falls upon the land is evaporated there, to 
return as rain in another place instead of being carried 
away by the rivers. On an area equal to the state of 
Wisconsin, for example, where the mean annual precipi- 
tation measures about 3 feet, the total fall must exceed an 
average of 40 acres of water 5 feet deep, for each minute 
of the year. But there are large areas of land where the 
mean annual precipitation is 60 inches, and others still 
where 8 feet of water fall : In these cases, for an area 
equal to the state of Wisconsin, or 56,040 square miles, 
the aggregate precipitation must exceed 8.5 40-acre-feet 
of water per minute in the first case, and 13.6 in the 
second. Now, on only a moderately fertile soil, the 
writer has grown maize, supplying it with water just as 
rapidly as it could use it to the best advantage, and 
found, as an average of two trials, that it did take, 
during its growing season, or one-third of a year, the 



Over and Over Again. 25 

equivalent of a rainfall of 34.3 inches, and produced a 
yield, when calculated for an acre, of more than four 
times a very large field crop grown under the best natural 
conditions of rainfall in Wisconsin; so that to grow a 
field of corn, of such quality, and the size of this state, 
would require the delivery of water upon it at the rate of 
40 acres more than 14 feet deep every minute during the 
growing season, or a rainfall greater than the largest con- 
sidered above. Large then as this movement of water is, 
it is seldom great enough during the growing season to 
enable a moderately fertile soil to produce its largest crops. 

But it is neither to the gaseous nor to the liquid por- 
tions of our earth that this process of over and over 
again is limited ; for even the solid land is profoundly 
involved in it. Careful measurement has shown that 
there goes to the sea annually, dissolved in the waters 
of the Mississippi Eiver, 150 million tons of rock ; and 
of these, 70 millions are the chief constituents of lime- 
stone — carbonates of lime, and magnesia ; so that the 
selfsame materials which journeyed to the sea, dissolved 
in the rivers of unnumbered centuries ago and laid down 
there by the action of marine life, have since become a 
part of the dry land, certainly once, if not many times, 
and are now journeying back to be rebuilt into the coral 
reef on the ocean's bottom yet once more. 

Nor is it rock and soil held in solution simply which 
water in its ceaseless rounds is bearing back to the sea ; 
for with the dissolved materials there is borne along as 
suspended sediment in the waters of the Mississippi 
alone, in the space of a single year, 362 million tons, 
making 513 million tons of rock and soil carried to the 
sea by one river, besides 750 million cubic feet of matter 
which are shoved along the bottom to form its delta. 



26 The Soil. 

The continual transfer of these large amounts of 
material from the land to the margin of the sea bottom, 
perpetually destroys the balance in the figure of the 
earth, so that the land areas rise to compensate in large 
measure for the materials borne away, while the marginal 
sea bottom subsides in like proportion to readjust the 
balance ; but as the sea sediments continue to subside, 
they become plastic under the great pressure to which 
they are subjected, and flow toward and under the rising 
land areas where denudation has been going on, so that 
in a very powerful but extremely slow manner there is 
a real movement of the solid land toward the sea above 
and from the sea back again to the land beneath. And 
if such profound and long-enduring systems of rotation 
as these are maintained as essential to the life of the 
world as a whole, we may practice with great confidence 
a rational rotation of crops in our systems of agricul- 
ture. 

Li We cannot measure the need 
Of even the tiniest flower, 
Nor check the flow of the golden sands 
That run through a single hour ; 
But the morning dews must fall, 
And the sun and the summer rain 
Must do their part and perform it all 
Over and over again. 

' ' Over and over again 
The brook through the meadow flows, 
And over and over again 
The ponderous mill-wheel goes. 
Once doing will not suffice, 
Though doing be not in vain." 



CHAPTER I. 

THE NATURE, FUNCTIONS, ORIGIN, AND WASTING OF 

SOILS. 

Of all commonplace things, it would be difficult to find 
one more uninteresting to most people than soil. Walk- 
ing over it all our lives, it has come to be, in our unre- 
flective moods, simply dirt, something essentially unclean 
and to be shunned. So deeply ingrained is this feeling 
that it comes to many almost as an inheritance, and 
people of culture, as well as the ignorant, find them- 
selves stoutly inclined to shun everything and every- 
body directly associated with it. 

But the spirit and results of investigation, which have 
grown so rapidly during our century, have already so 
widened our horizon of knowledge, and so changed the 
attitude of mind toward the phenomena of nature about 
us, that we are coming to study, in the spirit of science, 
many of those things which lie nearest to us, and with 
great moral, intellectual, and pecuniary profit ; and since 
soil, air, and water are indispensable to all forms of life, 
we must know more and more of them as the demands 
for food and homes increase. 

Taking samples of soil from where we will, whether 
from the fertile prairies of central North America, from 
the tundras of Siberia, from the barren wastes of the 
Sahara, or the rich river bottoms of the Amazon, every- 
where we shall find them composed of mingled fragments 

27 



28 The Soil. 

of materials of various kinds. Usually the soil is com- 
posed chiefly of small fragments of rock of many 
varieties, which may be regarded as the basis of them 
all. Associated with these fine rock remnants there 
is almost always a varying amount of organic matter 
derived from the breaking-down of vegetable and ani- 
mal remains. Then, too, adhering to the surface of 
these fragments, or scattered among them in the 
form of crystals, there are various substances which 
have been deposited from over-saturated solutions of soil 
moisture. 

In clayey soil there is present among its fine silt-like 
particles a small quantity of silicate of aluminum having 
water combined with it, and which gives to it its sticky, 
plastic, or putty-like quality. This adhesive clay, how- 
ever, forms only a small part of the whole weight of 
such soils, amounting to not more than 1.5 per cent, 
according to Schlosing. Then, too, the soils in many 
parts of the world have scattered through them larger or 
smaller blocks of stone, varying in size from great masses 
sometimes weighing tons, down through those which a 
man can barely move, to pebbles and coarse grains of 
sand. These fragments form no part of the soil proper, 
but instead are the materials out of which soils are 
made. It is true that the roots of plants may place 
themselves alongside of these coarse pieces of rock, and 
by their action derive some nourishment from them, but 
the amount thus obtained is insignificant when compared 
with that which an equal volume of soil might contribute 
if placed in their stead; so that such rock fragments, 
while they will contribute their volume of soil to the 
agriculture of the future, are a positive hindrance to that 
of the present. 



Surface Soil and Subsoil. 29 

SURFACE SOIL AND SUBSOIL. 

In humid climates, where the rainfall is sufficient to 
insure remunerative crops, it is common to speak of the 
surface, 6 to 12 inches of the fine rock fragments, 
as constituting the soil, while the deeper portions are 
spoken of as the subsoil, and this distinction grows out 
of the fact that' oftentimes when the deeper soil is 
brought to the surface, it is found to be unproductive for 
a time, and, besides, there is generally a sharp line of 
demarkation in the color of the two portions. In arid 
regions, however, where crops can only be raised by irri- 
gation, both of these distinctions largely or wholly dis- 
appear ; so much so that, in leveling fields to fit them for 
an easier distribution of water over the surface, little or 
no care is taken to avoid exposing the subsoil or covering 
even deeply the surface layer, experience having proved 
that earth from the bottom of cellars, and even that from 
depths of 30 feet, may be quite as productive, if not 
more so, than that which has been long exposed to the 
air. 

This difference in the nature of the deep soils of arid 
and humid regions appears to result from a variation 
either in the abundance or arrangement of the finest of 
the soil particles which exist in the deeper layers, the 
deeper soils of humid regions being usually more close in 
texture, and less easily penetrated by water. 

This difference in the texture of the soils of humid 
and arid regions is not confined to the subsoil, but 
involves the surface portions as well, so much so that 
when most soils of humid climates become dry, the sur- 
face is very hard and difficult to move, while those of 
the arid regions of the world are so incoherent that the 



30 The Soil. 

slightest puff of wind is sufficient to raise a dust, and a 
wind storm at any time is quite certain to raise great 
clouds of sand so characteristic of desert regions. 

Just why the soils of dry climates should lack in the 
amount of adhesive materials is not readily explained by 
unquestioned facts, but the condition appears to be in 
some way related to the larger amount of lime which 
Hilgard has shown these soils to contain. It has been 
abundantly proved by different experimenters that when 
the salts of lime are added to muddy water, it has the 
effect of enabling the silt particles to be gathered to- 
gether or to become flocculated, settling to the bottom 
and leaving the water clear, while without the addition 
of lime it would have remained turbid for an indefinite 
period. 

Hilgard has also shown by experiment that while any 
clay or tough clay soil, after being worked into a plastic 
mass and allowed to dry, acquires a texture of almost 
stony hardness, if to another portion of the same mass 
only half a per cent of caustic lime be added, a difference 
in the degree of plasticity is at once observable, and on 
drying the whole falls into a pile of crumbs at a mere 
touch ; and this change is assumed to result from the 
expulsion of the water of combination, from the grains 
of colloid clay, and the gathering of them together into 
compound particles of larger size, which then lose their 
cementing power. 

We do have, however, many clays very impervious to 
water, becoming, when worked, quite plastic and adhesive, 
but which cannot be used for brick or pottery on account 
of the large amount of lime they contain, which slacks 
after firing and by its expansion fractures the ware into 
which it has been shaped. Chemical analysis shows 



Relation of the Soil to Organic Evolution. 31 

such clays to contain in some cases as high as 5 per 
cent of lime and yet for some reason the clay has not 
lost its plastic character ; the lime has not produced the 
flocculation it sometimes does. 

Schlosing found, when he was trying to wash a soil 
with which he was working, until water would pass away 
from it clear, that, by passing a stream of carbon dioxide 
through the soil, it had the desired effect, and he attrib- 
uted the clearing of the filtered water to the formation 
of more soluble lime carbonate, which, by coagulating the 
fine clay passing the filter, causes it to be formed into 
compound clusters too large to escape. In view of this 
fact it may perhaps be urged that the lime once in the 
impervious clay could not be acted upon by the carbonic 
acid sufficiently to dissolve enough to do the work of 
flocculation, and also that soils more open, as those of 
arid regions must be when very dry, give easier and 
more complete access to both the carbonic acid and to 
what water does fall, so that with the usually relatively 
larger amount of lime present, owing to the less leaching 
in dry regions, enough would be dissolved to make a more 
complete coagulation than generally takes place in the 
soils of the more humid regions. 

RELATION OF THE SOIL TO ORGANIC EVOLUTION. 

But soil is very much more than a mass of broken and 
weathered fragments of inert rock, among which are 
strewn a small amount of the fast-decaying remnants of 
plant and animal life. To appreciate the mechanism of 
that great locomotive which in six days places the fruits 
of California on the tables of Boston, one must look at it, 
not cold and still, as so many nicely fitting pieces of 




Fig. 1. — Showing surface denuded of its soil by glacial action and not 

yet re-covered. 



Relation of the Soil to Organic Evolution. 33 

polished brass and steel, but alive, the great heart throb- 
bing, the strong arms at the wheels, and the monster 
starting, hurrying, halting, with its tons and tons of 
burden, always responding with the utmost promptness 
and the greatest exactitude to every beck and nod of the 
intelligence at the throttle. He must realize how, in its 
furnace open to the free air at both ends, the strength of 
forty horses is brought out of lifeless coal and placed in a 
chamber without an entrance doorway and only a chance 
to escape by doing work against the great piston heads. 
So if we will understand the soil, as farmers should, 
we must see it in action, helping on the work of the 
whole world as well as in producing the basket of apples, 
the bushel of wheat, or the pound of pork. 

How indispensable soil is to the life of both plants 
and animals as they are now constituted, will be apparent 
at a moment's reflection when we picture to ourselves the 
conditions which would exist were all the soil of the 
entire land area swept into the sea, leaving the surface 
with the appearance shown in Fig. 1. Under these con- 
ditions it is evident that all upright types of plants 
would be without means for maintaining that position, 
and there would be no provision, as these plants are now 
constituted, whereby they could be supplied with water 
except during times when the rains were actually falling ; 
for the water would hurry swiftly from the surfaces of 
the naked rock into the main waterways and off to the 
sea. 

Were the land without soil, the vegetation of these 
areas could only consist of a meagre growth of such 
forms, among living species, as now subsist upon the 
naked rocks of mountain sides and similarly exposed 
situations, where, for any reason, soil is not permitted to 



34 The Soil. 

accumulate; forms which, like the lichens, algae and 
fungi, are not provided with true roots, and which derive 
almost their whole nourishment, including water, directly 
from the air or from dead or living organic matter. 

Under such conditions as these it is plain that, for lack 
of food, if for no other reason, there could be no such pro- 
fusion of terrestrial animals as dwell in a land of plenty 
among us to-day. It is true that the tundras of arctic 
climates produce comparatively heavy crops of lichen 
growths such as the " Iceland moss," which, it is said, 
often forms the sole food of the poor inhabitants of that 
lonely land, like the " reindeer moss," which in northern 
Europe and in Siberia is the chief food of the reindeer 
and, in times of scarcity, ground and mixed with flour, 
that of man as well, and like the " Tripe de Boche," 
eaten by Indians and Canadian hunters in arctic North 
America. And then there is the " manna lichen " grow- 
ing on the arid steppes of the countries between Algiers 
and Tartary, which in times of drought and famine is used 
as food for large numbers of men and their domestic 
animals. But the luxuriance of growth in these cases, 
although small when compared with that of other vege- 
tation, is larger than it could be did it not grow lying 
upon the soil which holds the water to be given to the air 
about them by the more gradual process of evaporation as 
they need it. 

For not only does the soil make possible a very much 
greater profusion of land life than could otherwise exist, 
but it has also played an extremely important part in 
that long-continued, never-ending, and sublime process of 
evolution whereby, as lands have insensibly changed into 
sea and seas into land, as mountains have risen so slowly 
and silently out of level plains as to spring their broad 



Relation of the Soil to Organic Evolution. 35 

arches directly across wide rivers to the height of a mile 
and yet leave their courses unaltered, as climates have 
changed from cold to warm or from wet to dry, both 
plants and animals in this great drama of world action 
have been enabled to change, not simply their costumes, 
but if the exigencies of the new scene demanded it, legs 
for fins or even abandon them altogether and crawl upon 
their bellies through the grass. 

As the soil slowly became thicker and thicker, as its 
water-holding power increased, as the soluble plant food 
became more abundant, and as the winds and the rains 
covered at times with soil portions of the purely super- 
ficial and aerial early plants, the days of sunshine between 
passing showers, and the weeks of drought intervening 
between periods of rain, became the occasions for utiliz- 
ing the moisture which the soil had held back from the 
sea. These conditions, coupled with the universal ten- 
dency of life to make the most of its surroundings, appear 
to have induced the evolution of absorbing elongations, 
which by slow degrees and centuries of repetition came 
to be the true roots of plants as we now know them. 

When plants came to have specially organized absorb- 
ing surfaces placed in a supply of moisture which peri- 
odic rains made practically permanent and bounteous and 
which long contact with the finely divided soil grains 
kept continuously supplied with plant food not obtainable 
before, except in the most meagre quantities, the natural 
consequence to follow was a much more vigorous and 
larger growth of the parts above ground. 

But as bounteous feeding pushed the parts of plants 
higher above the surface of the ground, they were brought 
where they were obliged to withstand a much stronger 
wind pressure than when a precarious supply of moisture 



36 The Soil. 

kept them close to the surface, and hence, in order to sur- 
vive and utilize the new opportunities which a fertile soil 
affords, it became necessary to develop a stronger and 
more rigid tissue than the lower types of plants possess, 
and woody fibre in its various forms was the result. 

And then, with a deep, rich soil in regions of frequent 
and bounteous rains, with roots spreading wide and deep 
to gather and lift the percolating water, and with the 
woody structure of stem fixed, there began that race for 
sunshine which has led on and on from low to taller forms, 
each contestant in the battle striving always to lift and 
unfold its leaves in the sunshine and free air above all 
competitors, until there has resulted a vast array of for- 
est trees culminating in the giant Sequoias of our Pacific 
coast, some of which have attained a measured height 
exceeding 20 rods or 352 feet. 

The soil has made possible succulent, nutritious grass, 
great forest trees and flowers with beautiful petals, fra- 
grant odors and sweet nectars, while, with the slow evo- 
lution of these forms, there has come into being, to use 
them and to contribute to their welfare in return, the 
cattle and horses of the plains, the birds and squirrels of 
the forests, and the bees and butterflies which, guided by 
the colors and the fragrance they have learned to know, 
reach the nectar the flowers have provided for them that 
they shall be sure to come and distribute the pollen and 
secure to the plants, by cross-fertilization, that renewed 
vigor so essential to them. 

THE SOIL A SCENE OF LIFE AND ENERGY. 

In the agricultural sense it should be observed that the 
most important use of soil is to act as a storehouse of 



The Soil a Scene of Life and Energy. 37 

water for the use of plants, and that the productiveness 
of any soil is determined in a very large degree by the 
amount of water it can hold, by the manner in which that 
water is held, and by the facility and completeness with 
which the plant growing in it is able to withdraw that 
water for its use as it is needed. But while this state- 
ment is true in the fullest sense, it must not for a moment 
be thought that the composition of the soil is not an im- 
portant factor in fixing land values for crop production. 
The great importance of the water-holding power grows 
out of the fact that without an adequate supply of water, 
neither the other food constituents which the soil con- 
tains, nor that larger part which is derived from the air, 
can be procured by the plant, nor transformed or assimi- 
lated by it. 

Then, again, the soil is a wonderful laboratory in which 
a large variety of the lower microscopic forms of life are 
at work during those portions of the year when its 
temperature is above freezing, breaking down dead or- 
ganic matter and converting it into those forms in which 
it again becomes available for plant food ; and the farmer 
should never forget that the crop of these invisible organ- 
isms which are produced each year in his soil, determines 
in no small degree the magnitude of the harvest he re- 
moves from the ground and the fitness of that ground for 
a succeeding crop. 

Finally, the soil is a means for transforming sunshine 
and putting it into a form available for carrying on 
the kinds of work which are there accomplished, and 
the manner in which the soil is tilled and the way it is 
fertilized have much to do with the quantity of altered 
sunshine which becomes available in carrying on this 
work. 



38 



The Soil. 



INFLUENCE OF ROCK STRUCTURE IN SOIL 
FORMATION. 

There are many agencies at work in the production of 
soil, and the process is one which is being carried forward 
continuously night and day and almost incessantly the 




Fig. 2. — A thin section of mica schist, showing the crystalline struc- 
ture which lends itself to the conversion of rock into soil. 

year through. It is taking place in the tilled field and 
in the meadow ; in the depths of the forest and on the 
prairie ; in the driest desert regions of the world and 
under the tropics where rains are of daily occurrence ; in 
the polar regions and under the equator and on the top- 



Influence of Rock Structure in Soil Formation. 39 

most summits of mountain masses as well as along the 
margins of the lake and the sea, or where streams at 
times rise and overflow their banks. 

Nearly all rocks are made up of fragments or crystals 
of various sizes and kinds, and these are bound together 
more or less firmly by some cementing material, but 
usually there are places which have not been completely 
filled with the cement, and these give to most rocks a 
certain degree of permeability to water. Granite, for 
example, has been found to absorb nearly .4 of a pound 
of water to each 100 pounds of rock, and the fine-textured 
agate is open enough to admit of coloring by capillary 
absorption. Fig. 2 conveys a general idea of that struc- 
ture of rocks here referred to, and which lends itself so 
readily to their conversion into fine fragments and ulti- 
mately into soil. 

When such rocks are brought to the surface, where 
they are exposed to wide ranges of temperature, the 
different rates of expansion possessed by the different 
minerals entering into their structure tend to loosen them 
and open the natural cavities wider. Into these cavities 
the rain water is drawn by capillarity, and on freezing 
tends to open the cavities still more, and to flake off 
from the surface minute fragments, adding so much to 
the soil. Then as the rocks by this action become more 
porous, the rain water, holding carbon dioxide in solution, 
enters more freely and dissolves the more soluble min- 
erals, and, as the surface dries, these dissolved materials 
are brought out and washed away by the rain or blown 
off by the winds, thus leaving the rock more and more 
porous until finally it falls into fragments, illustrated so 
well and so frequently by what are popularly called 
" rotten stones." 



40 



The Soil 



In moist and warm climates the solvent power of water 
here referred to, is exerted with the greatest vigor, but 
in damp, cold countries the effects of freezing are most 
apparent, while in desert regions neither the one nor the 
other become soil-producing agents of any note. 




Fig. 3. — Showing the conversion of rock into soil on a limestone hilh 

Whoever will visit an abandoned stone quarry where 
the rocks have lain undisturbed for ten or twenty years ; 
will readily observe in the stained and altered surfaces, 
in the softer, more easily scratched outer layer, and in the 
slight accumulations of soil, which the rains and the 




Fig. 4. — Showing the transition from rock to soil on a limestone plane. 



winds have swept into the small inequalities of the rock, 
the initial process of soil formation as it is still taking 
place and has been throughout geologic ages. 

Passing from the abandoned quarry to some fresh cut 
along the railway or roadside, where a hill has been 



Influence of Rock Structure in Soil Formation. 41 

graded down, there may be seen at the top the finished 
soil, and between it and the unaltered glacial gravel or 
original rock below, as the case may be, every degree of 
progress from the one into the other, represented in Tigs. 
3 and 4, where the first shows the stages of transition as 




Fig. 5. — Showing advanced state of erosion. Giant's Castle near 
Camp Douglas, Wisconsin. 

they have taken place over the summit of a limestone 
hill, while the second shows the same facts for a more 
level limestone surface. 

Then, again, the rocks of almost any quarry, on exam- 
ination, will be found to be divided into blocks of varying 



42 



The Soil. 



size and form by fissures or breaks, which owe their 
origin to a general shrinkage of the surface layers and to 
small but ever-present benclings or wave-like motions of 
the ground. These features are well brought out in 
Figs. 5 and 6, and they introduce us to another process 
in the formation of soil. 




Fig. 0. — Showing the last stage of the conversion of cliffs into soil. 



Such fissures as these, when not too deeply covered 
with soil, are often penetrated by water and by the roots 
of trees. Then as the water freezes and as the roots 
grow, both expand with an almost irresistible power and 
open the old crevasses wider or make new breaks where 



Running Water as a Soil Builder. 43 

none existed before, thus dividing the larger blocks into 
smaller ones, and often throwing the fragments to the 
foot of the cliff, where they soon become overspread with 
a mantle of vegetation under which they rapidly fall 
into soil. This process as it is carried forward in nature 
may be better appreciated by carefully studying Fig. 7. 

Those who live near the foot of great rocky cliffs 
which are subject to this sort of action of ice, like the 
quartzite cliffs at Devil's Lake, Wisconsin, are frequently 
startled during cold nights in winter by loud reports 
followed by the sound of rolling stone as great blocks of 
rock, sometimes many tons in weight, snap under this 
action of frost and go bounding down the steep face of 
the pile of angular fragments which have accumulated 
at the foot under the same action many times repeated. 
Then, again, where a great tree has grown up with its 
roots reaching deep into some wide fissure filled with 
soil, on the summit of an overhanging or vertical cliff, 
it not unfrequently happens that a strong wind from 
the right direction, pressing against the wide-spreading 
boughs and using the tall trunk as a lever, pries off sec- 
tions of the cliff, sometimes 20 feet long, as many deep, 
and 6 to 10 feet thick. Such a block the writer has 
known to fall during a wind storm. 

RUNNING WATER AS A SOIL BUILDER. 

Running water is another agent which, by processes 
peculiar to itself, has done very much in the production 
of soil and in giving to it certain characteristics. Stand- 
ing on the bank of any small stream and watching the 
water as it slides over the bottom, it will be seen that 
there are incessantly being moved along the bed, some- 




M 



A 



6 



Running Water as a Soil Builder. 45 

times rolling, sometimes sliding, grains of sand of vary- 
ing sizes. One set moves on for a short distance and 
then stops, other grains follow after but halt at the same 
place until a small but appreciable ridge is formed. 
Similar tiny ridges are forming on its right and on its 
left, some above it and others below. But these are only 
brief resting places ; for a change in the velocity of the 
current as the waters shift from side to side causes each 
ridge to move another step farther down the stream. 
But as the grains roll, tumble, and slide by turns in their 
downward course, each has its corners worn away, each is 
growing insensibly but surely smaller, and each is con- 
tributing something to that impalpable powder, which, 
rising into the body of the stream, remains suspended for 
almost indefinite periods except in the stillest water, 
where it is laid down in lakes or carried to the sea to 
slowly subside and become beds of clay, and when those 
geographical changes come which drain a lake or elevate 
the margin of the sea bottom into dry land, it then 
becomes fields of clayey soil. 

But what becomes of the grains of sand which are 
only moving along step by step, and where was their 
resting place before they joined this caravan traveling 
toward the sea? A little observation will soon show 
where their journey begins. Following along the bank 
until a bend in the stream is reached, it will be at once 
observed that the concave side of the channel is deep, 
while the convex side is shallow. On the concave side 
the current is swift and plainly cutting away the bank, 
which now rises abruptly above the water, or perhaps 
has come to be so far overhanging that a portion has 
already broken loose and slid into the stream, where the 
rapid current is sorting out the grains it is able to move 



46 The Soil. 

along and bearing them beyond the turn. But on the 
convex side the ground slopes gently almost to the 
water's edge ; the current is feeble, and hence the grains 
of sand advancing from above are here being laid down 
to fill the channel on this side as rapidly as the stream 
cuts away the bank on the other. The bed of a stream, 
then, is constantly shifting ; soil is being taken from one 
side and borne along for a distance and then laid down 
upon the other, where it constitutes a new soil, and will 
remain as such until the stream sweeps back once more 
across its valley. Looking at Fig. 8, which is a map of 
a portion of the Mississippi below Vicksburg, it is 
plainly shown how the action at the bends here referred 
to is being carried on, the dotted areas in the channel 
showing where the deposits are taking place, and the 
clear portions where the banks are being crowded back. 
There is one thing about this map, however, which it 
is not so easy to comprehend, and that is the amazing 
extent to which this great river is to-day sauntering 
about upon its alluvial plain, some 40 miles in width, 
as shown by Lakes Bruin, Palmyra, and St. Joseph, 
which are only great ox-bow portions of its channel 
which it has recently abandoned. Colonel Abbot says of 
these shiftings of the river : " Chief among such changes 
is the formation of cut-offs. Two eroding bends ap- 
proach each other until the water forces a passage 
across the narrow neck. As the channel distance 
between these bends may be many miles, a cascade, 
perhaps 5 or 6 feet in height, is formed, and the tor- 
rent rushes through it with a roar audible for miles. 
The banks dissolve like sugar. In a single day the 
course of the river is changed, and steamboats pass where 
a few hours before the plow had been at work." The 



Running Water as a Soil Builder. 47 




Fig. 8. — Showing the shiftings of a river channel as it forms alluvial 

soils. 



work here is of course extraordinary, as it must be 
when the run-off from more than 1,200,000 square miles 



48 The Soil. 

is brought together into one channel on a plain which 
falls only one inch in 40 rods, and over which it winds 
some 1100 miles in making a distance south of less than 
half that number. 

While such extreme windings as these are confined to 
large rivers where they traverse very flat stretches of 
country, this shifting of the streams, this picking up of 
soil from one place and laying it down in another, is 
nevertheless very general and very extensive ; and when 
we speak of the Mississippi as carrying to the Gulf, 
suspended in its waters or shoved along its bottom, 
every year soil enough for 72 sections of land 4 feet 
deep, this work is small when compared with that which 
measures the shifting of sand from side to side by the 
same stream even after it passes the city of Memphis ; 
and vast as this work can but be, it must constitute a 
standard all too small by which to measure that which 
in the aggregate is done throughout the broad valley of 
the Ohio, the Upper Mississippi, and the Missouri, with 
their tributaries. Glance for a moment at Fig. 9 that 
it may be realized, not only how many times the Madison 
fork of the Missouri River must have crossed and re- 
crossed its broad valley, but how many times over and 
over again it must have handled that soil before it suc- 
ceeded in carrying out of its field of labor the amount 
which the unimpeachable testimony of those terraces 
show it has transported to loAver levels. Think also 
how, again and again, a new vegetation must have 
taken possession of the reworked land, as the soil was 
being transferred now to the right bank and now to the 
left. Years and years, and even centuries, must have 
passed before a given field was entirely replowed, 
resoiled, and reseeded ; but everywhere in the past and 







K 



7t 



73 






73 



bfi 

o 

CO 



M 



50 Tlie Soil. 

everywhere in the present tins long-time rotation has 
been and is now being carried on by the ceaseless action 
of rivers. 



WORK OF RAIN. 

Besides the action upon the soil, of running water, 
which we have considered, after it has reached the 
perennial waterways, there is a large mechanical work 
performed by the rain while on its way over the surface 
toward the streams or before entering the ground to 
emerge again in the form of springs. At the time of 
heavy rains the surface of the ground, even on rather 
steep slopes, becomes covered with a sheet of water, and 
the raindrops, striking into this and upon the soil, work 
up the looser grains so that, as the water moves down the 
inclines, it bears along with it over shorter or longer dis- 
tances a considerable body of soil. In cultivated fields, 
especially where the soil has a tine texture and the prop- 
erty of losing its coherence when flooded with water, 
the amount of soil moved at such times on the more 
rolling lands is very large indeed. 

Whoever has the opportunity to traverse the uplands 
in the state of Mississippi to-day will be confronted with 
a gigantic but sorrowful example of what this action of 
rain may accomplish in the brief period of thirty years 
on such soils as are here referred to. I quote the lan- 
guage of W. J. McGee, who has made a careful study of 
this region : — 

" With the moral revolution of the early sixties came 
an industrial revolution ; the planter was impoverished, 
his sons were slain, his slaves were liberated, and he 
was fain either to vacate the plantation or greatly to 



Work of Main. 51 

restrict his operations. So the cultivated acres were aban- 
doned by thousands. Then the hills, no longer pro- 
tected by the forest foliage, no longer bound by the 
forest roots, no longer guarded by the bark and brush 
dam of the careful overseer, were attacked by raindrops 
and rain-born rivulets and gullied and channeled in all 
directions ; each streamlet reached a hundred arms into 
the hills, each arm grasped with a hundred fingers a 
hundred shreds of soil, and as each shred was torn away, 
the slope was steepened and the theft of the next storm 
made easier. 

" So, storm by storm and year by year, the old fields 
were invaded by gullies, gorges, ravines, and gulches, ever 
increasing in width and depth until whole hillsides were 
carved away, until the soil of a thousand years' growth 
melted into the streams, until the fair acres of ante-bellum 
days were converted by hundreds into bad lands, desolate 
and dreary, as those of the Dakotas. Over much of the 
upland the traveler is never out of sight of glaring sand 
wastes where once were fruitful fields ; his way lies some- 
times in, sometimes between, gullies and gorges, the ' gulfs ' 
of the blacks whose superstitions they arouse, sometimes 
shadowed by foliage, but oftener exposed to the glare of 
the sun reflected from barren sands. Here the road 
winds through a gorge so steep that the sunshine scarcely 
enters ; there it traverses a narrow crest of earth between 
the chasms, scores of feet deep, in which he might be 
plunged by a single misstep. When the shower comes, 
he may see the roadway rendered impassable, even oblit- 
erated, Avithin a few minutes ; always sees the falling 
waters accumulate as viscid brown or red mud torrents, 
while the myriad miniature pinnacles and defiles before 
him are transformed by the beating raindrops and rushing 



52 The Soil -^ 

rills so completely, thai when tho^sun shines again he 
may not recognize the nearer landscape. 

" This destruction is not confined to a single field or 
a single region, but extends oveaCmuch of the upland. 
While the actual acreage of soil tlms destroyed has not 
been measured, the traveler through the region on horse- 
back daily sees thousands or tens of thousands of for- 
merly fertile acres now barren sands ; and it is probably 
within the truth to estimate that 10 per cent of upland 
Mississippi has been so far converted into bad lands as 
to be practically ruined for agriculture under existing 
commercial conditions, and that the annual loss in real 
estate exceeds the revenues from all sources ; and all 
this havoc has been wrought within a quarter century. 
The processes, too, are cumulative ; each year's rate of 
destruction is higher than the last. 

" The transformation of the fertile hills into sand wastes 
is not the sole injury. The sandy soil is carried into the 
valleys to bury the fields, invade the roadways, and con- 
vert the formerly rich bottom lands into treacherous 
quicksands when wet, and blistering deserts when dry. 
Hundreds of thousands of acres have thus been destroyed 
since the gullying of hills began a quarter of a century 
ago. Moreover, in much of the uplands the loss is not 
alone that of the soil, i.e. the humus representing the 
constructive product of water work and plant work for 
thousands of years ; but the mantle of brown loam, most 
excellent of soil stuffs, is cut through and carried away 
by corrasion and sapping, leaving in its stead the in- 
ferior soil stuff of the Lafayette formation. In such 
cases the destruction is irremediable by human craft — 
the fine loam, once removed, can never be restored. 
The area from which this loam is already gone is ap- 



Work of Rain. 53 

palling, and the rate of loss is increasing in geometric 
proportion." 

It is not necessary, however, to go to the bad lands of 
Mississippi or the Dakotas for examples of this work ; for 
every carefnl farmer has witnessed it a hundred times on 
every hillside of his farm, and has studiously tried to 
prevent it. But this action of rain is much more general 
and in the aggregate much greater than has yet been indi- 
cated ; for it takes place, only in a less intense and less 
obtrusive way, over the surface of all except swamp and 
the most heavily wooded lands, always moving the sur- 
face soil from the higher toward the lower grounds and 
ultimately to within the reach of streams. 

When the soils of hillsides expand with increasing 
moisture or with frost, there is a small but sure move- 
ment downward, for while the push is equal in all 
directions, the downward thrust has the force of gravity 
on its side ; and the same movement results when the 
soil comes to shrink after drying, for it is easier to draw 
the upper particles down than to pull the lower ones up. 
Blocks of stone, too, lying upon the slope, expanding in 
the hot sun and contracting during the night, tend to 
creep insensibly into the valley. When the fox, and the 
many burrowing animals of whatever sort, bring dirt to 
the surface, or when great forest trees are uprooted by 
the storm, the soil moved is without exception left one 
step nearer to the sea. It is evident that by whatever 
one of these methods of creeping the soil is moved, the 
rate of travel will, other conditions being the same, 
always be most rapid on the steepest slopes, so that 
generally this action must result in the soils of the 
summits or high lands crawling down and upon those 
of the lowlands, producing an overplacement which gives 



54 



The Soil 



to the soils of the invaded areas characteristics derived 
from the rocks whose destruction contributed the material 
for the overplacing soil. For the same reason, too, the 
resultant soils will usually be found more fertile and 
more enduring, as every farmer knows, than that left 
behind on the more sloping ground. The general facts 
of soil creeping and of overplacement are indicated dia- 
grammatically in Fig. 10. 



Poor Soil 



Rich Soil 




Fig. 10. — Showing movement of soils from higher to lower levels. 



GLACIAL SOILS. 

In those portions of the world where the temperature 
is so low that most of the moisture is frozen when it 
falls and does not all melt during the summer, the snow 
accumulates often to great depths and by its weight is 
compressed into ice. When snow in this condition has 
attained a considerable thickness, it begins to move along 
sloping surfaces much as liquid water does, converging 
into larger and larger streams, moving faster where the 
slope steepens and slackening its speed again when the 
descent becomes less. In Fig. 11 is shown one of these 
ice streams descending from the Alaskan mountains 
toward the Pacific Ocean, where it had its birth. 



Glacial Soils. 



55 



While the movements of glaciers are much less rapid 
than those of rivers, their far greater depth and con- 
sequent heavy pressure, together with the more rigid 
nature of the ice, give to these streams a grinding, 




Fig. 11. — Showing an Alaskan glacier. 

scoring, and transporting power which is great almost 
beyond measure ; and hence it is that in mountain dis- 
tricts, which rise above the line of perpetual snow, and 
in the frigid zone, glaciers become soil-producing agents 
of great vigor. 



56 The Soil 

In very recent geologic time, during the glacial epoch, 
a vast ice sheet gathered in the higher latitudes and 
spread from the direction of northern Labrador until 
it overran two-thirds of the North American continent, 
advancing so far southward as to place its front in the 
shape of a rude crescent, stretching from Cape Cod and 
Long Island through northern Pennsylvania into the 
Ohio valley and from thence, following the course of this 
stream and that of the Missouri River, to the Rocky 
Mountains. At the same time there appears also to 
have been on the Pacific slope a lesser and apparently 
more local sheet, which pushed itself southward through 
the mountain valleys until it passed the foot of Puget 
Sound. 

What conditions conspired to induce this long geologic 
winter has not yet been learned, but during its prevalence 
the snows piled upon the land until a mantle hundreds 
and perhaps thousands of feet in thickness overspread 
the whole area outlined above, while the general level of 
the ocean fell as its waters were drawn upon to feed the 
ever-deepening snow fields as they spread over the north- 
ern continents of the Eastern and Western Hemispheres 
alike. As the specific gravity of ice varies between .917 
and .922, the mean weight of a cubic foot will exceed 57 
pounds, and an ice sheet 10 feet in depth will press upon 
its bed with a weight exceeding 570 pounds to the square 
foot, while the burden imposed by 500 and 1000 feet of 
ice must exceed 28 and 57 thousand pounds to the square 
foot, or 198 and 396 pounds to the square inch respec- 
tively. What a mill for grinding rock into soil we have 
here ! For its nether stone one-half or two-thirds of the 
North American continent, and for its upper one a block 
of ice of corresponding size, five hundred to a thousand 




£ 






ft 

so 

p 

o 

CO 



o 

M 



58 The Soil 

and more feet thick, having its grinding face thickly set 
with sand and gravel, and those same hard bowlders, 
large and small, which we now find strewn so thickly 
over the surface and through the soil of this whole gla- 
ciated area, while the two faces were set against each 
other with a pressure exceeding 200 to 400 pounds to the 
square inch and quite probably double these amounts ! 
With such a mill as this, set up under no other roof 
than the dome of a cold arctic sky, and run incessantly 
day and night, year in and year out, for centuries, 
numbered certainly by hundreds if not by thousands, 
a great work must have been accomplished. 

During all this time the great ice sheet was creeping 
slowly toward the south and southwest, its whole front, 
from the Atlantic to the Rocky Mountains, now advanc- 
ing a little and now retreating as variations in the rate 
of travel or the rate of melting occurred. Beneath the 
bottom of this slowly moving sheet of pressure-plastic 
ice, which, with more or less difficulty, kept itself com- 
formable with the face of the land over which it was 
riding, the sharper outstanding points were cut away 
and the narrower and deeper river canons filled in. 
Desolate and rugged rocky wastes were ground down and 
overspread with rich soil, and regions with sandstone for 
the surface rock, which by decay in place could give only 
lands of the lighter type, became mantled with thick 
layers of mixed gravel, sand, and clay, forming by slow 
alteration rich and enduring soils. 

Great streams of water emerging from the melting ice 
sorted and resorted the glacial grist, leaving in some 
places extensive beds of coarse, clean gravel with surfaces 
sloping gently in the direction of discharge, over which 
has since developed one type of extremely fertile prairie 







o 

CO 






60 



The Soil. 



soil; leaving in other places beds of sharp plastering 
sand, often interstratified in the most curious and abrupt 
manner with coarser or finer materials, while the finest 
silt was farther removed to subside in innumerable lakes, 
formed by glacial dams, or to be borne away to the sea to 
contribute materials for the extensive deposits of our 
coastal plains. 

When the ice front tarried long at a given place, the 




Fig. 14. — Showing glacial scratches on north shore of Kelley's Island, 

Lake Erie. 



broken and worn fragments of rock continually brought 
along by the ice were unloaded there, as it melted, until 
great irregular ridges were formed, sometimes several 
miles wide and from 20 to 400 feet in height, and these 
have been named terminal moraines. Mingled with these 
huge piles of rock, sand, and gravel there were left, at 
the time of the final retreat, great blocks of ice, and when 
these finally melted and the water drained away, they 
left the surface of the moraine thickly set with deep and 



Earthivorms as Soil Workers. 61 

abrupt hollows, to which the name of kettles came to be 
applied ; and Fig. 12 shows, as well as a picture can, a 
surface thus formed, while Fig. 13 represents a section of 
one of these morainic hills which was cut through in 
grading for a railroad. 

In very many parts of the country overrun at this 
time, the harder and more enduring kinds of rock often 
still show with remarkable distinctness the actual course 
the ice stream took by the scratches, grooves, and furrows 
which were left in the polished surface of the rock made 
by stone, gravel, and grit imbedded in the bottom of the 
glacier. An illustration of such a rock surface is repre- 
sented in Fig. 14. And, since these rock surfaces have 
sufficiently withstood all other methods of rock decay to 
enable them to retain these records for so long a time as 
has intervened between the close of the glacial period and 
the present time, it is evident that glacial action must be 
ranked as the greatest soil-producing agent of recent 
geologic time. 

EARTHWORMS AS SOIL WORKERS. 

Then there are many animals which have contributed 
largely to rock grinding and soil formation. Many will 
recall the great number of piles of earth which angle- 
worms bring to the surface after heavy rains, and espe- 
cially during the spring and early summer when the 
ground is wet. Their method of action is this : in mov- 
ing through the soil, they eat a narrow hole, swallowing 
the earth, when the point of the head is held fast in this 
excavation while an enlarged portion of the esophagus or 
swallow is drawn forward forcing the cheeks outward in 
all directions, thus crowding the soil aside and making 



62 



The Soil 



the opening wider, when more dirt is eaten and the proc- 
ess repeated. After the swallowed earth has been worked 
over in the muscular gizzard and the organic matter 
associated with it digested, it is passed from the body, 
but while in the stomach the grains of sand suffer a con- 
siderable amount of 
wear, much as is the 
case with pebbles 
and bits of glass 
eaten by poultry and 
all seed-eating birds 
for the purpose of 
grinding their food. 
Charles Darwin, 
who made a very 
long and careful 
study of this action 
of earthworms, came 
to the conclusion 
that in many parts 
of England these 
animals pass more 
than 10 tons of 
dry earth per acre 
through their bodies 
annually, and that 
the grains of sand 
and bits of flint in 
these earths are partially worn to fine silt by the action 
of the gizzards of these animals ; but this extensive 
action is not peculiar to England, for the species of earth- 
worms have a wide geographic distribution, and Fig. 15 
represents a soil chimney made by a species in India, 




Fig. 15. — Showing a tower-like casting 
ejected by a species of earthworm 
from the Botanic Garden, Calcutta. 
Natural size. Engraved from a photo- 
graph after Darwin. 



Earthworms as Soil Workers. 



63 




Fig. 16. — Showing the work of the common earthworm during a single 
night after a heavy rain. 



64 The Soil 

while Fig. 16 shows the work of a single night on a Wis- 
consin farm after a heavy rain. 

HUMUS SOILS. 

There is a class of soils in which humus is the dom- 
inating characteristic, and these have their origin in 
swamps of various types. In many parts of the world, 
but especially in high latitudes or at considerable eleva- 
tions, where the surface is too flat for rapid and com- 
plete drainage and where the winter snows remain so long 
that the duration of summer is insufficient to dry the soil 
enough for it to become readily penetrated by the air, 
there comes to be formed a deposit of humus or peat, min- 
gled with varying proportions of mineral grains. When 
soil is allowed to become dry and at the same time porous, 
so that air has an unlimited access to it, all organic mat- 
ter which it may contain is rapidly and completely re- 
turned to the atmosphere, as is illustrated in an emphatic 
manner in the use of the dry-earth closet; but when 
organic matter falls upon an over-saturated soil, or be- 
neath the surface of water, there is so slow an access of 
oxygen to the decaying matter that only a partial decom- 
position takes place, which results in the formation of 
the black or brown humus so characteristic of swamp 
soils. It frequently happens during the development of 
soils of this type that heavy forest growths are slowly 
drowned out by it as it accumulates in thickness and 
more and more completely excludes the air from the 
roots of the trees. 

Under other conditions, where a great river like the 
Mississippi, the Nile, or the Ganges approaches its outlet 
or winds over a flat plain, it so builds up the bottom of 



Humus Soils. 65 

its channel, by laying down the sediments which it car- 
ried with ease over the steeper portions of its course, as 
to place it higher than the adjacent flats ; and then, in 
times of frequent overflow, the adjacent country is 
periodically flooded, and the water, not finding ready 
return to the river, furnishes the conditions for the 
growth of aquatic plants and a swamp soil begins to 
form. Then again when rivers change their course, as 
in the case of the formation of ox-bows already referred 
to, there result shallow lakes with muddy bottoms in 
which aquatic plants are quick to spring up and begin 
the formation of a rich humus which in later years may 
lead to no little wonderment as to how such a soil in such 
a shape could have had its origin. The swamp soils of 
river origin, when they are drained and dry, on account 
of the sand and silt mingled with the humus, fall among 
the richest, most enduring, and quickest to respond to 
agricultural treatment. 

If one will study a detailed map of almost any portion 
of North America lying north of the great glacial front, 
to which we have referred, he will be surprised at the 
very large number of small lakes there shown ; and then 
if he could see a good soil map of the same section, he 
would be still more surprised, not only at the even 
greater number of small and large irregular isolated 
areas of swamp soil, but also at the extent of the fringes 
of these soils, which are shown bordering most of the 
lakes. The isolated areas of swamp soil were once lakes 
themselves, which, after partial drainage and the forma- 
tion of marginal muddy flats by the wearing down of 
their outlets, began the development of humus first over 
the flats through the growth of aquatic plants rooted 
on the bottom, and later, as the deeper water was 



66 



The Soil. 



approached, by a rapid spread of these and the sphagnum 
moss extending around the lake as a floating fringe. 
As this sphagnum continues to grow above and die below, 
with only partial decay, it settles deeper into the water 
and finally rests upon the bottom. Or if the lake is 
deep, the growth may advance steadily toward the centre 
until finally the whole is overgrown. Upon this raft of 
aquatic vegetation the sedges begin to grow, small wil- 
low and heath-like plants follow, and finally, when a 
sufficient thickness has been formed, the tamarack dis- 
putes the ground and covers the whole with a forest of 
straight green spires. As these trees grow to maturity 




Fig. 17. — Showing the passage of a lake into a peat hed and swamp or 

humus soil. 



and the tall shafts fall to be buried in shrouds of anti- 
septic sphagnum, the whole lake cover grows thicker, 
heavier, and finally comes to rest upon the bottom. 
Fig. 17 shows a section of a lake passing through the 
stages here described. 

It not infrequently happens in these lakes, during the 
overgrowing period, that large areas of the floating peat 
break away and drift from side to side, impelled by the 
wind acting upon the vegetation as a sail. Such a de- 
tachment, consisting of several acres, occurred in 1875 
in Lake Butte des Morts, through which the Fox River 
passes before entering Lake Winnebago in Wisconsin. 
This field of swamp grass drifted against a long railroad 



Humus Soils. 67 

bridge, threatening its destruction, and had to be cut with 
ice saws into blocks small enough to clear the water- 
ways. 

On the shores of the larger lakes and along the mar- 
gins of the sea, the waves often throw up bars of sand, 
cutting off lagoons whose waters, in the case of the sea, 
by the shutting out of the tides, come to be converted 
first into brackish and then fresh-water lakes and finally 
into areas of swamp soil. And then when the sea has a 
flat or gently sloping tidal plain over which the water 
rises more than one or two feet, deposits of peat begin to 
form in the sheltered bays through the growth of certain 
grasses which have acquired the power of thriving in salt 
water. Starting at the shore line, they advance by de- 
grees toward the sea as the tidal sediments gather about 
their feet, building the bed of peat up to near the level 
of high tide, and in this way forming extensive deposits. 
This work is very materially assisted, as Shaler has 
shown, by the occasional breaking-up of these peat de- 
posits through the action of waves and the redepositing 
of them in deeper water, where they constitute a soil 
upon which a peculiar flowering plant, the eel grass, has 
acquired the habit of living entirely submerged beneath 
the water. This plant, playing the same part in the deeper 
water below low-tide mark which the grasses do above 
it, gathers silt and builds up a platform upon which the 
grasses may advance in their work of winning land from 
the sea ; and the amount done since the glacial period, 
along the New England coast alone, is placed by Shaler 
at more than 350,000 acres, while the total area of 
marine marshes, which owe their formation to grass- 
like plants, the same writer places at nearly 10,000 
square miles in the United States. But the most inter- 



68 The Soil. 

esting and important fact about these lands is, that, like 
those of Holland, when won from the sea and made fit 
for tillage, they become extremely rich and enduring 
soils. And then to think that all this potential wealth 
of food, happy, industrious homes, and moral lives should 
lie unused in the very shadow of a great city where so 
many thousands are worse than starving, where so much 
wealth is seeking profitable investment, and where so 
many charitable hearts are yearning to see some path- 
way leading away from those dens of misery ! Why may 
not intelligence, wealth seeking investment, charity and 
poverty join hands in converting those great stretches 
of waste land close by their doors into the richest acres, 
where the poor who will may not only find employment, 
but earn a garden and a home, with all these can mean ? 

WIND-FORMED SOILS. 

There is still another method and another agency by 
which soil building and soil wasting are carried on. It 
is probable that nowhere can soils be found which do not 
contain larger or smaller amounts of wind-borne particles, 
— particles which have traveled unknown distances, and 
these often very great. There is never a raindrop falls, 
never a hailstone reaches the ground, and never a snow- 
flake, however white, but which brings to the soil it 
moistens one or more particles of dust. The streaks of 
dirt left upon the window pane with the melting of snow 
which has drifted against the glass are a sufficient proof 
to the housewife of the truth of the statement just made, 
while the color of rain water and the sediment which 
both it and the water of melted snow leave when evapo- 
rated to dryness, bear witness to the same facts. 



Wind-formed Soils. 69 

But it is in arid regions more particularly and along 
sandy coasts, that this action of the wind as a soil builder 
and soil destroyer is most marked. On the leeward mar- 
gins of arid regions sand-drowned forests, as well as cities 
and ancient monuments, stand as silent witnesses of this 
abraiding and transporting power of the wind. The 
most extensive formations ascribed to the action of winds 
are some types of a deposit which have been named loess. 
Richthofen describes a formation of this character in 
China as a wholly unstratified calcareous clay of a very 
fine texture, which contains many land shells, bones of 
land animals, and land vegetation. The formation as 
described by him has a wide distribution, and attains 
a thickness in places of loOO and possibly 2000 feet. 
It should be stated here, however, that formations very 
similar to this have a much wider geographic distribu- 
tion, being found extensively both in Europe and North 
America, but these are so related to ancient glacial mar- 
gins and channels of overflow as to suggest, for them at 
least, an apparently different origin. 

When we call to mind the experience we all have had 
regarding the accumulations of wind-driven dust which 
collect in abandoned houses and in rooms even when un- 
occupied for only brief periods, when we recall the clouds 
of dust raised from the road and from the surfaces of 
light, dry soils, or watch the snow as it is driven from 
field to field, we need not be surprised if the wind has 
done a great work where it has had an unimpeded sweep 
and the years of geologic time at its disposal. 



CHAPTER II. 

TEXTURE, COMPOSITION, AND KINDS OF SOILS. 

We have seen that almost everywhere the land surface 
is overspread with a mantle of rock fragments, sometimes 
large but mostly very small, the upper portion of which 
has been designated the soil. We have pointed out that 
this soil is a water reservoir in which the rains are caught 
and held, that it is a great laboratory in which certain 
essential plant foods are being made, and that deeply into 
it the roots of plants grow for support, moisture, and 
nourishment. 

SOIL TEXTURE AND ITS INFLUENCE. 

In looking at the texture of the soil, so far as the size 
of its grains is concerned, we may consider the valuable 
results obtained by Hilgard in his mechanical analysis 
of some Mississippi soils. By his method of treatment 
he has so separated the grains of soil of different kinds 
as to bring those having the same diameters together, 
thus enabling him to determine the percentage amounts 
of each size entering into the particular soil. The diam- 
eters of the soil grains and the percentage amounts of 
each size, as they occur in a sandy soil and subsoil from 
the long-leaf pine plateau in Smith County, are given 
below : — 

70 



Soil Texture and its Influence. 71 



DIAMETER. 

3937 to 4724 hundred thousandths of an inch 

2362 to 3937 " " " 
1575 
1181 

610 " " " 

472 " " " 

283 " " " 

185 " " " 

142 " " " 

98 " " " 

59 " " " 

31 " " " 

A tt tt It 

In two other soils, one a " Hog-wallow " subsoil from 
Jasper County, very clayey and difficult to work, and 
another a loess soil from Claiborne County, we have 
diameters and relative proportions as given below : — 



Soil. 
Per Cent. 


Subsoil. 
Per Cent. 


.4 


.4 


3.0 


.8 


6.9 


6.3 


8.1 


3.4 


3.0 


3.9 


1.6 


1.5 


1.2 


.6 


3.6 


2.6 


6.8 


5.4 


14.6 


7.9 


14.8 


17.0 


30.7 


38.3 


4.6 


10.9 



Diameter. 








Clay 

Subsoil. 

Per Cent. 


Loess 

Soil. 

Per Cent, 


3937 to 4724 hundred thousandths of 
2362 to 3937 


an inch 

1 1 


.8 
1.2 


I- 2 


1575 


tt 


tt 


tt 


2.0 


.4 


1181 


(t 


tt 


tt 


1.6 


.6 


610 


U 


tt 


tt 


.9 


.9 


472 


l< 


tt 


tt 


.3 


1.7 


283 


(C 


tt 


1 1 


.2 


2.0 


185 


tt 


tt 


1 1 


2.5 


14.3 


142 


It 


tt 


tt 


3.7 


16.2 


98 


tt 


tt 


tt 


5.6 


20.1 


59 


tt 


tt 


tt 


10.6 


5.6 


31 


tt 


tt 


1 1 


24.7 


33.6 


4 


tt 


tt 


tt 


48.0 


2.5 



The values given in these tables have great significance 
in showing, first, how it is that soils can act as water 



72 The Soil 

reservoirs of great capacity ; second, how even when they 
are made up very largely of materials extremely difficult 
of solution, they may, when kept supplied with an abun- 
dance of water, dissolve in large quantities ; and third, 
how it is that the roots of plants are brought into very 
intimate contact with an immense surface of soil grains. 

If you plunge a marble into water, and then withdraw 
it, it comes forth surrounded by a film and the greater 
the surface of the marble the larger will be the amount 
of water which adheres to it. When the rains saturate 
any soil, the surface of each soil grain has its film of 
water as in the case of the marble. It is not difficult to 
see how reducing the diameters of soil grains, greatly 
increases the number of them in a cubic inch, and at the 
same time increases the total soil surface to which the 
soil water may adhere. Suppose we take a marble exactly 
one inch in diameter. It will just slip inside a cube one 
inch on a side and will hold a film of water 3.1416 square 
inches in area. But reduce the diameters of the marbles to 
one-tenth of an inch and at least 1000 of them will be 
required to fill the cubic inch, and their aggregate sur- 
face area will be 31.416 square inches. If, however, the 
diameters of these spheres be reduced to one-hundredth 
of an inch, then 1,000,000 of them will be required to 
make a cubic inch, and their total surface area will then 
be 314.16 square inches. Suppose again the soil parti- 
cles to have a diameter of one-thousandth of an inch. It 
will then require 1,000,000,000 of them to completely 
fill the cubic inch, while their aggregate surface area 
must measure 3141.59 square inches. 

Turning back to the tables which show the observed 
sizes of grains obtained by the mechanical analyses, it will 
be noted that the smallest of them have diameters placed 



Soil Texture and its Influence. 73 

at .00004 of an inch, a size far below the last we have 
considered, and yet a cubic foot of soil grains having a 
diameter of .001 of an inch will provide a surface for 
holding water, as we have seen the marble do, equal to 
37,700 square feet. Four feet in depth of such a soil, a 
depth to which the roots of most farm plants penetrate, 
would possess a water-holding surface not less than 3.4 
acres for each column of soil one square foot in section. 
An extremely thin film, therefore, on such a surface, must 
aggregate a large amount of water, and we need not be 
surprised to learn that only moderately fine-grained soils 
have been observed to retain in the surface five feet, 
under field conditions, no less than the equivalent of 12 
to 20 inches of water on the level. 

It should be observed here, regarding the very small 
size of grains shown in the tables of mechanical analyses 
given above, that it is extremely improbable that the 
smallest of them are individually invested by films of 
water as these occur undisturbed in the soil. On the 
contrary, future study seems likely to demonstrate that 
even the stiffest clay soils are made up of complex 
grains, into which the capillary waters do not freely 
pass, and that the extreme division shown by present 
methods of mechanical analysis are in part the result of 
a breaking down of compound grains which, under field 
conditions, act largely as if they were solid particles of 
greater size. These statements are made here to caution 
the reader against carrying the computations made above 
by the writer much farther than he has done. 
*- Turning now to the influence of the texture of the 
soil on its ability to supply the soluble ash ingredients 
needed by the vegetation growing upon it, it will be at 
once apparent that the broad surface which the soil 



74 The Soil 

water has been shown to cover must lead to a rapid 
solution of soil material and a relatively rapid produc- 
tion of plant foods, when they are present, even though 
they may exist in the soil in forms soluble with extreme 
difficulty. 

An instructive experiment has been made by the 
French chemist Pelouze, aiming to illustrate the influence 
of a fine state of division, or of small particles, on the 
rate of solution. In a flask holding a little more than 
a pint, he kept water boiling constantly during five days, 
and at the end of this time he emptied, dried, and weighed 
the flask, finding it to have lost less than two grains in 
weight. He next broke off the neck of the flask ; grind- 
ing it to a fine powder and returning it to the body of 
the flask, he repeated the boiling during five more days. 
At the end of this time he found that fully one-third 
of the total weight of his flask had been dissolved by the 
water. 

Storer states that the Messrs. Rogers found, by digest- 
ing powdered feldspar, hornblende, and various other 
minerals with water for/ a week, that from a third of 
one per cent to one per cent of the mineral was dissolved 
out by the water. Taking the lowest estimate, namely 
one-third of a pound of mineral for each one hundred 
pounds of the dry powdered rock, and multiplying the 
result by the weight of soil in the surface foot of an acre 
of land, we find that more than 10,000 pounds might be so 
dissolved during one week. But Voelcker has shown 
that 15 tons of good well-rotted manure to the acre will 
supply no more than 150 pounds of potash and 140 
pounds of phosphoric acid to the acre. 

It is undoubtedly true that the rate of solution here 
cited is much more rapid than ever occurs in natural 



Soil Texture and its Influence. 75 

soils, but the work may go forward more or less rapidly 
during the whole year and throughout a depth of more 
than live feet, and still be within the reach of root action ; 
and more than this, it is probable that the state of divis- 
ion in the soil much exceeds that which obtained in 
the experiment of the Messrs. Rogers. It is not strange 
therefore that, where due attention has been paid to 
rotation of crops and where a fair amount of organic 
matter in the form of stable manure has been supplied, 
many soils have been found practically inexhaustible 
even under centuries of cropping. 

When we bear in mind that the roots of our cultivated 
plants penetrate the soil to a depth of four or more feet, 
that they extend horizontally away from the steins 
through an equally great distance, and that throughout 
all of this broad and deep mass of soil innumerable and 
extremely minute root hairs thread their way among 
the soil grains and come in touch with them throughout 
their whole length and on all sides, we are confronted 
with the great work which is conjointly done by the 
sunshine, the plant, and the soil. Viewed in this light, 
soil is not a grave where death and quiet reign, but 
rather a birthplace where the cycles of life begin anew, 
to run their courses over and over again. 

There are some soils which, in their minuter structure, 
are made up of extremely small particles, but which are 
nevertheless so coarse-grained as to be more or less leachy 
in character and to possess a quality of easy tillage 
approaching that of sandy land. The loess soils are a 
type of these, and they contain a large number of com- 
pound grains in which the minute particles have been 
cemented with carbonates of lime and magnesia into 
small concretions which behave, so far as the texture of 



76 The Soil. 

the soil is concerned, as though they were in reality 
grains of sand. There must also be some of this sort of 
structure in the more open types of clay soils, and it is 
probable that the underdraining of such lands tends to 
augment this tendency to granulation and thus improve 
their quality. Stiff, clayey subsoils, too, have a tendency 
to shrink and draw together into small cube-like blocks, 
particularly during dry seasons and especially after 
they have been underdrained, and this structure facili- 
tates in a marked manner complete drainage, thorough 
aeration and a deeper penetration of the roots of plants 
into them. Such an opening up of a clay soil as this 
makes it possible for the carbonic acid of soil water to 
dissolve lime and bring it into contact with the deeper 
and stiff er clays, and, by its flocculating or granulating 
tendency, to so improve their texture, in the course of 
years of proper tillage, as to render them more produc- 
tive and more easily worked. 

CHEMICAL CONSTITUENTS OF SOILS. 

From what has been said regarding the origin of soils, 
it will be evident, at once, that whether we look at them 
from the standpoint of the chemical elements which 
enter into their composition, whether we enumerate the 
chemical compounds which a thorough analysis might 
reveal, or whether we attempt to name the various min- 
erals which time and the agents of geologic change have 
brought together, we must expect to find almost any soil 
a body of extreme complexity, so far as its composition 
is concerned. The fact that few indeed, if any, of the 
minerals entering into the rock structure of land masses 
are wholly insoluble, even in pure water, the fact that 



Chemical Constituents of Soils. 



77 



this water carries its dissolved materials both through 
and across the surface of the soil and over long distances, 
and the fact that the movements of the surface waters, 
winds, and burrowing animals of all kinds and even 
plants work together in mixing and transporting soil 
particles, must tend to give to all soils, wherever they 
may be found, a general composition which is extremely 
similar. 

Of the many chemical elements occurring in the soil, 
those which have the greatest abundance, or are of most 
importance from the standpoint of agriculture, are named 
below : — 



Non-Metals. 


Metals. 


Oxygen. 


Chlorine. 


„ Aluminum. - Sodium. 


Silicon. 


^ Phosphorus. 


Calcium. Iron. 


Carbon. 


„ Nitrogen. 


- Magnesium. Manganese, 


Sulfur. 


Fluorine. 


t Potassium. 


Hydrogen. 


Boron. 





Oxygen occurs in the soil in the free state and in com- 
bination with all of the elements named except fluorine. 
Silicon, combined with oxygen, forms silica or quartz, so 
familiar to us in the form of plastering sand, pebbles 
of quartz, carnelian, and jasper. So abundant is silica 
or quartz that it is estimated to compose more than one- 
half of the known rocks of the earth. Because it is so 
difficultly soluble and so hard, quartz, in larger or smaller 
particles, is the chief ingredient by volume and by 
weight of nearly all soils everywhere. 

Carbon occurs in the soil as a part of the humus or 
organic matter, united with calcium and with magnesium 
in the form of carbonates, and also united with oxygen 
in the form of carbon dioxide as one of the soil gases 



78 The Soil 

and which, dissolved in the soil water, plays so impor- 
tant a part in the solution of plant food. But the plant 
gets the carbon of its food from the free carbon dioxide 
of the air. 

Sulfur occurs in the soil in the form of sulfids united 
with iron or as sulfates united with some metal, as 
iron, lime, or magnesia. United with oxygen and calcium, 
it forms land plaster or gypsum, an important fertilizer ; 
it is also an essential part of many organic compounds 
in the tissues of plants and animals. 

Hydrogen plays its greatest part in agriculture, and in 
the life of the world, while combined with oxygen in 
the form of water, and it is in the form of water that 
plants get most of the hydrogen and oxygen which go 
to make up their tissues and the starches, sugars, and 
other forms of stored food. 

Chlorine is neither a large constituent of soil nor one 
which plays a very important part in its work. It is 
usually associated with sodium in the form of common 
salt, which occurs in all soils, in all natural waters, and 
even in rain. Chlorine is uniformly found in the com- 
position of plants, and is regarded as in some way 
essential. 

Phosphorus, which in its uncombined state is used 
in the manufacture of matches, because it so readily 
ignites in the presence of oxygen, is never found in the 
soil or in nature except combined with some other sub- 
stance. It is very generally distributed in the soil, 
though not in large quantities, but is a very essential 
soil ingredient. It occurs as a constituent of the oldest 
known rocks and from these, through the processes of 
rock decay and rock building, it has been ever present 
in the soils of all geologic ages. Through the action 



Chemical Constituents of Soils, 79 

of plants it is gathered up from the soil and concen- 
trated in their tissues ; animals in their turn, feeding 
upon the plants, or upon other animals, concentrate the 
compounds of phosphorus still farther, so that now the 
remains of animal life in rock deposits are valuable 
sources of commercial fertilizers, and man, through his 
intelligent effort, is taking advantage of these ancient 
concentrations of plant food by bringing them forth and 
redistributing them where they may be used over again 
in carrying forward once more the life processes of the 
present day. 

Nitrogen, though the most abundant element in the 
atmosphere, is one of the least abundant in the crust of 
the earth as a rock ingredient. In the soil, in the com- 
bined form, it occurs as a part of humus and the fragments 
of the decaying tissues of plants and animals, from which, 
through the instrumentality of microscopic life there, it is 
converted ultimately into nitric acid, which, uniting with 
potash, lime, or other soil ingredients, forms a soluble 
salt taken up by the roots of plants and is then made to 
yield up its nitrogen to build those nitrogenous compounds 
so abundant in the tissues of animals. 

Neither boron nor fluorine have any considerable abun- 
dance in soils, and their percentage composition in the 
ash of plants is small. Borax is the most familiar com- 
pound in which boron occurs. Fluorine, united with 
lime, occurs in Iceland spar, and it is a constituent of the 
blood, milk, teeth, and bones of mammals. 

Aluminum is placed third in abundance among the 
elements of the surface ten miles of the solid land. It is 
a beautiful white metal, remarkably light, and does not 
readily tarnish. While it is not a plant food, it is a 
fundamental constituent of true clay, which is derived 



80 The Soil. 

from the breaking-down, by chemical action, of feldspar, 
mica, and other constituents of granitic rock; and it is 
important to keep in mind that the true clays, and the 
fine clay -like particles play a very important part in de- 
termining the texture and water-holding power of soils. 

Calcium and magnesium are two metals very closely 
associated, and, united with carbon dioxide, they consti- 
tute the limestone beds of the world. Magnesium is an 
indispensable plant food, as is also lime. Both collect 
largely in the seeds of plants, the magnesia more abun- 
dantly than the lime, wheat containing 12 per cent in its 
ash of magnesia, as against 3 per cent of lime, while the 
ashes of peas contain 8 per cent of the former to 4 per 
cent of the latter. If phosphorus is counted a very im- 
portant plant food because it occurs in the seeds of plants, 
the same reasoning would be applicable to both lime and 
magnesia, but both of these substances occur in most soils 
in much larger quantities than does phosphorus, and be- 
cause of this their need is not so often felt. 

Potassium is one of the very essential elements of plant 
food, and although it is almost universally distributed in 
soils, the compounds which it forms are usually so sol- 
uble that there is a strong tendency for them to leach 
away and to be borne to the sea in the drainage waters. 
On account of this characteristic of the potash salts, bad 
management leads to a rapid depletion of the soil stores of 
this element and a corresponding shortage in the yields of 
crops. Potash occurs widely distributed in the earth's 
crust, largely as a constituent of orthoclase feldspar and 
the biotite and muscovite micas. In certain places, too, it 
occurs in the mineral glauconite of the greensands of New 
Jersey and elsewhere, and also in certain layers of the 
potsdam sandstone in various parts of the world. The 



Chemical Constituents of Soils. 81 

glauconite sometimes composes as much as 90 per cent of 
the greensands and is itself made up of 8 to 12 per cent 
of potash. Potash, too, is also a notable constituent of 
kaoline beds, those in Wisconsin showing an average 
per cent of 1.975 for fifteen analyses. 

Kepeatedly, in geologic history, movements of the 
earth's crust have shut off arms of the sea, whose waters 
afterward evaporated, leaving very rich and extensive 
deposits of those salts which were carried in solution by 
the ocean waters ; and among these were laid down 
vast beds of kainite which are now being mined and 
returned as fertilizers to the land, where the potash is 
used over again. The ashes of land plants are rich in 
potash as a carbonate, and, united with nitric acid, it is 
produced in the soil in the form of nitre. 

Sodium is the basis of common salt, and as such has a 
world-wide distribution. It very much resembles potas- 
sium as an element but can in no sense take its place in 
the life of land plants. In the form of Chili saltpetre 
sodium nitrate is largely used as a fertilizer, but for the 
nitric acid it contains rather than for the sodium. 

Iron and manganese are two of the most abundant of 
the heavy metals and occur almost universally as constit- 
uents of the soil, but the former in much larger quantities 
than the latter. Iron, united with oxygen and with 
water, constitutes the red and yellow ochres used so much 
as pigments in painting, and which give to soils their red 
and yellow colors. Iron, too, is an important plant food, 
although it does not enter largely into the composition of 
their tissues. It is so abundant, so universely present in 
the soil, and so difficultly soluble that there is never a 
deficiency of it so far as the purposes of the plant are 
concerned. 



82 The Soil. 

If we look at the composition of soils as shown by chemi- 
cal analysis, it will be observed that while there is a strong 
likeness among them all, to which reference has been 
made, there are nevertheless quite wide variations among 
them, so far as the relative proportions of the constitu- 
ents are concerned; and the truth of this statement will 
be readily appreciated from the tables on pages 84-87, 
which are taken from the papers of Hilgard in the tenth 
census of the United States. Selecting for comparison 
the most widely divergent types, so far as physical con- 
ditions are concerned, we have set against the sandy 
soils the heavy clays. 

That these analyses may have as great significance as 
possible, brief descriptions of the soils are given in the 
order in which they occur in the table, and the sandy soils 
are first described under the numbers used by Hilgard. 

No. 36. Little Mountain soil, Alabama. Native vege- 
tation, chestnut, short-leaf pine, hickory, post oak, and 
small sourwood. Depth 8 inches; color, top soil, dark 
brown 2 inches ; yellowish sand at 2 feet and at 5 feet 
solid sandstone rock. 

No. 11. Chunnenugga ridge soil, Alabama. Depth, 6 
inches. Vegetation, chestnut, short-leaf pine, red oak, 
and sour gum; color, dark gray, changing at 6 inches to 
a lighter gray, and at 3 feet to a yellowish color. 

No. 8. Pine upland soil, table-land, Florida. Vege- 
tation, long-leaf pine, round and narrow leaf, black-jack, 
red and post oaks, and hickory. Soil taken at a depth of 

9 inches. Subsoil, a yellowish sand, with slight inter- 
mixture of yellowish clay, becoming a hard yellow clay at 
a depth of 2 to 6 feet. 

No. 7. Gray, sandy pine woods soil, Florida. Depth, 

10 inches. Vegetation, long-leaf pine and wire grass. 



Chemical Constituents of Soils. 83 

No. 142. Gray, sandy soil, Georgia. Taken 6 inches 
deep. Vegetation, red and post oak, pine and hickory. 

No. 322. Dark, sandy, upland soil, Georgia. Taken 
6 inches deep. Timber growth, hickory, oak, and long- 
leaf pine. 

No. 359. Gray, sandy soil, Georgia. Depth about 6 
inches, with yellow sandy subsoil. 

No. 252. Dark, sandy soil, Georgia. Depth, 6 inches, 
underlaid at a depth of a few feet by white marl beds. 
This and No. 359 are described as oak, hickory, and pine 
uplands. 

No. 307. Gray, sandy soil of oak and hickory lands, 
Georgia. Sarsaparilla in abundance. Depth, 6 inches. 

No. 165. Gray, sandy soil, Georgia. Depth, 6 inches. 
Vegetation, long-leaf pine. 

The clay soils are as follows : — 

No. 98. Post-oak and flatwoods clay, Alabama. 
Depth, 10 inches, reddish clay, spotted. Vegetation, 
chiefly post oak. 

No. 149. Red clay soil, Georgia. Vegetation, red, 
white, and post oaks, dogwood, chestnut, hickory, and 
pine. Depth,- 5 inches. 

No. 203. Deep red soil, Georgia. Growth, red and 
post oak and hickory. Depth, 8 inches. 

No. 166. Red hill lands, Georgia. Taken 6 inches 
deep. Vegetation not given. 

No. 513. Ash-colored clayey swamp land, Georgia. 
Growth, cypress, water oak, gum, ash, maple, beech, 
and saw palmetto. Blue clay stratum at 1 to 6 feet. 

No. 10. Yellowish red clay, South Carolina. Timber, 
post, white, and black oaks, short-leaf pine, and hickory. 
Depth, 5 inches. 

No. 141. Stiff red soil from the cretaceous prairie 



84 



The Soil. 



CHEMICAL COMPOSITION OF SOILS. 



Numbers. 


Insoluble 

Residue. 


Soluble 
Silica. 


Total Insoluble 

Residue and 
Soluble Silica. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


36 

11 • 
8 
7 
142 
322 
359 
252 
307 
165 


98 
149 
203 
166 
513 

10 

141 

390 

1 

7 


93.630 
94.770 
93.362 

95.630 
92.0! 10 
90.230 
90.681 
92.460 
94.428 
94.822 


72.746 
73.690 
60.370 
73.422 
(53.444 
77.860 
54.565 
51.063 
79.580 
75.350 


1.682 

.486 

1.721 

.879 

1.220 

1.940 

1.885 

1.550 

.529 

1.037 


8.926 

3.370 

2.000 

2.709 

11.325 

1.790 

13.219 

20.704 

3.628 

7.310 


95.312 
95.256 
95.083 
96.509 
93.310 
92.170 
92.566 
94.010 
94.957 
95.859 


81.672 
77.060 
62.370 
76.131 
74.769 
79.650 
67.784 
71.767 
83.208 
82.660 


Averages 




93.210 


68.209 


1.293 


7.498 


94.503 


75.707 








374 




91.498 




1.722 




93.220 



SWAMP AND LOESS SOILS. 



Humus. Loess. Humus. Loess. Humus 



Averages i 35.886 68.853 20.825 4.918 56.711 73.771 



Loess. 



SOILS COMPARED WITH THEIR SUBSOILS. 

SOILS. 




Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Averages 


93.222 


73.978 


1.019 


5.034 


94.241 


79.012 








SUBSOILS. 


Averages 


90.714 


66.290 


2.212 


7.446 


92.926 


73.736 






Differences 


+2.508 


+7.688 


—1.193 


-2.412 


+1.315 


+5.276 


ARID AND HUMID SOILS COMPARED. 




Humid. 


Arid. 


nurnid. 


Arid. 


Humid. 


Arid. 


Averages 


84.031 


70.565 


4.212 


7.266 


87.687 


76.135 

















Chemical Composition of Sails. 85 

CHEMICAL COMPOSITION OF SOILS. — Continued. 



NUMBEBS. 


Potash. 


Soda. 


Lime. 


Magnesia. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


36 


98 


.100 


.416 


.060 


.112 


.120 


.080 


.040 


.691 


11 


149 


.156 .176 


.069 


.004 


.081 


.090 


.069 


.112 


8 


203 


.045 


.186 


.018 


.119 


.064 


.071 


.005 


.065 


7 


166 


.117 


.134 


.064 


trace 


.058 


.219 


.042 


.289 


142 


513 


.110 


.242 


.035 


.079 


.090 


.387 


.025 


.508 


322 


10 


.067 


.092 


.009 


.041 


.119 


.036 


.090 


.070 


359 


141 


.275 


.431 


.130 


.277 


.055 


.540 


.048 


.836 


252 


390 


.095 


1.104 


.036 


.325 


.076 


1.349 


.083 


1.665 


307 


1 


.209 


.150 


.069 


.065 


.141 


3.054 


.031 


.029 


165 


7 


.034 


.255 


.022 


.258 


.045 


.340 


.043 


.296 


Averages 


.121 


.319 


.051 


.128 


.085 


.617 


.048 


.456 


| 374 




.137 




.054 




.173 




.203 





SWAMP 


AND 


LOESS 


SOILS 










Humus. 


Loess. 


Humus. 


Loess. 


Humus. 


Loess. 


Humus. 


Loess. 


Averages 


.639 


.435 


.109 


.165 


3.786 


5.820 


.886 


3.692 



SOILS COMPARED WITH THEIR SUBSOILS. 

SOILS. 





Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Averages 


.157 


.214 


.072 


5.08 


.115 


1.761 


.076 


.182 



SUBSOILS. 



Averages 


.143 


.344 


.064 


.085 


.096 1.481 


.073 


.240 


Differences . . . 


+.014 


-.130 +.008 


.000 


+ .019 


+.280 


+.003 


-.058 





ARID 


AND HUMID 


SOILS 


COMPARED. 








Humid. 


Arid. 


Humid. 


Arid. 


Humid. 


Arid. 


Humid. 


Arid. 


Averages 


.216 


.729 


.091 


.264 


.108 


1.362 


.225 


1.411 



86 



The Soil 



CHEMICAL COMPOSITION OF SOILS. — Continued. 



Numbers. 


Brown Oxide 

of Manganese. 


Peroxide 
of Iron. 


Aluminum. 


Sand. 


Clay. 


Sand. 


Hay. 


Sand. 


Clay. 


Sand. 


Clay. 


36 

11 

8 

7 

142 

322 

359 

252 

307 

165 


98 
149 
203 
166 
513 

10 

141 

390 

1 

7 


.102 
.156 
.220 
.049 
.126 
.313 
.172 
.040 
.101 
.020 


.106 

.146 
.19(5 
.164 
.052 
.056 
.079 
.119 
.195 
.038 


.761 
.706 
.941 
.224 
.963 
1.927 
1.837 
.843 
.661 
.930 


12.406 
5.989 
9.709 
4.054 
3.894 
5.646 
7.089 
5. SI 8 
3.420 
5.784 


1.532 

.733 

1.339 

.473 
1.959 
2.141 
1.436 
2.649 
1.195 
1.576 


2.473 

7.305 

18.066 

10.598 

13.454 

7.538 

16.071 

10.539 

4.988 

5.567 


Averages 


.130 


.115 


.979 


6.381 


1.503 


9.660 




374 




.066 




1.372 




1.522 



SWAMP AND LOESS SOILS. 



Averages. 



Humus. 



.098 



Loess. 



.164 



Humus. 



7.040 



Loess. 



3.569 



Humus. 



14.476 



SOILS COMPARED WITH THEIR SUBSOILS. 

SOILS. 




Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 




.124 


.133 


1.162 


5.205 


1.145 


6.998 


SUBSOILS. 


Averages 


.080 


.125 


1.739 


6.947 


2.276 


12.086 


Differences 


+ .044 


+ .008 


-.577 


-1.742 


—1.131 


-5.088 


ARID AND 


HUMID SOILS COMPARED. 






Humid. 


Arid. 


Humid. 


Arid. 


Humid. 


Arid. 


Averages 


.133 


.059 


3.131 


5.752 


4.296 


7.SS8 



Chemical Composition of Soils. 



87 



CHEMICAL COMPOSITION OF SOILS. — Concluded. 



NUMBEBB. 


Phosphoric 
Acid. 


Sulfuric 
Acid. 


Water and 
Organic Mattkk. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Clay. 


36 


98 


.051 


.103 


.028 


.061 


2.055 


1.906 


11 


149 


.101 


.071 


.057 


.055 


2.642 


8.891 


8 


203 


.066 


.204 


.091 


.285 


2.422 


8.953 


7 


166 


.092 


.069 


.058 


.035 


1.807 


8.309 


142 


513 


.191 


.071 


.105 


.055 


3.477 


6.843 


322 


10 


.111 


.082 


.054 


.054 


2.881 


6.167 


359 


141 


.105 


.187 


.034 


.009 


3.682 


6.922 


252 


390 


.039 


.304 


.045 


.024 


2.354 


7.369 


307 


1 


.103 


.242 


.046 


.089 


3.113 


4.962 


165 


7 


.014 


.079 


.035 


.079 


1.636 


4.962 


Averages 


.087 


.141 


.055 


.075 


2.607 


6.528 




.374 




.088 








3.394 



SWAMP AND LOESS SOILS. 



Averages . 



Humus. 


Loess. 


Humus. 


Loess. 


Humus. 


.150 


.200 


.148 


.090 


13.943 



SUBSOILS. 



Loess. 



1.205 



SOILS COMPARED WITH THEIR SUBSOILS. 

SOILS. 





Sand. 


Clay. 


Sand. 


Clay. 


Sand. 


Ciay. 


Averages 


.128 


.207 


.052 


.090 


2.853 


6.014 



Averages 


.124 


.159 


.060 


.071 


1.943 


4.780 


Differences. . . . 


+ .004 


+ .048 


-.008 


+ .019 


+ .910 


+1.234 



ARID AND HUMID SOILS COMPARED. 





Humid. 


Arid. 


Humid. 


Arid. 


Humid. 


Arid. 


Averages 


.113 


.117 


.052 


.041 


3.644 


4.945 



88 The Soil. 

region, Mississippi. Fairly productive in good seasons. 
Vegetation, oak. 

No. 390. Buckshot soil of Yazoo bottom, Louisiana. 
Stiff dark-colored clay soil, mottled with spots of ferru- 
ginous matter, traversed by numerous cracks. Very 
fertile and no change in character to a depth of 10 feet. 
Vegetation, sweet gum, pecan, water and willow oak, 
hackberry, and honey locust. 

No. 1. Red clay land from central basin, Tennessee. 
Vegetation, hickory, red, white, and post oaks, elm, ash, 
honey locust, black walnut, wild cherry, sugar trees, 
poplar, hackberry, redbud, dogwood, and papaw. Depth, 
7 inches, with heavy clay subsoil. 

No. 7. Same region, depth, and vegetation as No. 1, 
but subsoil not as heavy. 

If reference is made to the table showing the chemical 
composition of sandy soils as compared with that of clay 
soils, it will be seen that during the process of analysis 
31.791 per cent of the soil ingredients were dissolved 
out of the clay, as shown by deducting the 68.209 per 
cent of insoluble residue from 100, while only 6.790 
per cent were dissolved from the sandy soils, making a 
difference of 25.001 in favor of the clay soil. In the 
average, too, of the ten different analyses, it will be 
seen that the various soluble ingredients are shown to 
be dissolved more abundantly from the clayey than from 
the sandy soil. 

How shall these results be understood? Do they mean 
that in every 100 pounds of sandy soil, plants may find 
nearly 7 pounds of soluble material, the larger part of 
which is plant food, while in the clayey soil there are 31 
pounds in each and every 100, or more than four times as 
much? Do they mean that clay soils are capable of yield- 



Chemical Composition of Soils. 89 

ing the ash ingredients of plant food to growing crops 
four times more rapidly than sandy soils can do? Or, 
are we to understand that the ash ingredients of plant 
food in clay soil are being carried away by the waters 
which percolate through them four times more rapidly, 
gallon for gallon of water, than they are from the sandy 
soil? 

If the results of the chemical analyses of soil were to 
be taken without qualification, one or the other of these 
conclusions would seem to follow, but it is very unfor- 
tunate for agriculture that it should seem necessary to 
admit that the results of soil analyses, as they have 
been made, can and do throw but a very dim and uncer- 
tain light upon either the condition or the amount of 
available plant food a soil may contain. The results of 
chemical analyses do show, beyond question, that there 
are marked differences between soils, but so far as the 
data now at hand can be interpreted, these variations, 
at least so far as the mere relative proportions of the 
so-called soil ingredients are concerned, seem quite as 
likely to be due to differences in the actual sizes of soil 
grains, as to any real and marked difference in either the 
chemical or mineralogical composition of them. 

When given quantities of coarse and fine grained soils, 
having identical chemical composition, are subjected to 
like quantities of dissolving acid, under like conditions, 
it would appear to follow necessarily that, where all of 
the materials are not dissolved, and where a complete 
saturation of the solvent has not resulted, more mate- 
rials will enter into solution from the fine than from the 
coarse grained sample ; and simply because more points 
of attack are presented by one than by the other. With 
like quantities of soil and acid, the solution would not be 



90 The Soil. 

directly proportional to the total surface areas in the 
two samples, because in the fine-grained sample, where 
the solution is most rapid on account of the greater sur- 
face, the strength of the acid would be most rapidly 
reduced, thus tending to make the ratio between the 
quantities dissolved somewhat less than the ratio between 
the areas of the soil grains in the two samples. 

If it should occur that certain kinds of soil grains in 
both cases were more easily and completely dissolved 
than the bulk of the soil materials, then the ratio, in 
such cases, between the dissolved materials would be 
less than between the surfaces of the original soil grains. 
So, too, unless very vigorous stirring were constantly 
maintained, the fine-grained soil would tend to dissolve 
less rapidly in proportion to its surface than would the 
coarse-grained soil, where diffusion would be relatively 
more rapid. 

But in spite of the condition just referred to, the much 
larger surface area possessed by the two, three, or more 
grams of clay soil taken for analysis appears to have 
resulted in extracting a relatively larger amount of plant 
food from this soil than was removed from the more 
coarse-grained and relatively small-surfaced sandy soil. 

If we compare the mechanical analyses of the two 
Mississippi soils, Nos. 390 and 377, as given by Wiley, 
with their chemical analyses, as given by Hilgard, it will 
be found that, while the surface area in one gram of the 
fine soil is about seven times that of the one of coarser 
grain, the soluble materials extracted were only about 
four times as large, thus making the rate of solution, 
when compared by equal surface areas, less for the clay 
than for the sand. So, too, if we take the mean surface 
area in one gram of twelve truck subsoils, of Maryland, 



Chemical Composition of Soils. 91 

as given by Whitney, and compare this with the mean 
area of one gram of six strong wheat subsoils, we shall 
find their surface areas to be in the ratio of 934 to 3451, 
while the ratio between the soluble ingredients of the 
sandy and clayey subsoils, as given on pages 84-87, 
is 9.286 to 33.71, or very nearly the same as that between 
the surface areas of the soil grains in the similar cases 
cited. 

The reader should bear in mind that these remarks 
are not intended to convey the idea that the chemical 
composition of sandy and clayey soils are nearly iden- 
tical, but rather that it seems more than probable that 
the ratio between the more difficultly soluble and the 
more readily soluble ingredients of plant foodj is not as 
widely different in the coarse and fine grained types of 
soil as the table of chemical analyses would appear at 
first thought to indicate. 

There has been placed in the table, just below the line 
of averages for soils, the analysis of a clay soil, No. 374, 
from Louisiana, which shows a relative proportion of 
the more soluble ingredients bearing a striking resem- 
blance to the more sandy types, the insoluble residue 
being 91.498 per cent, while that of the sandy soil aver- 
ages 93.210, there being two samples in the series of ten 
having as low a per cent of "insoluble residue " as 90.6. 
Hilgard describes this as a fair upland soil, yielding 
700 to 800 pounds of seed cotton per acre, color gray, 
depth 6 to 8 inches, not heavy, and underlaid by a subsoil 
quite heavy in tillage and dark orange in color. The 
case is cited to illustrate how a chemical analysis alone 
does not always serve to distinguish between soils which 
in their physical features may be strongly contrasted. 

If we look at the differences between the indicated 



92 The Soil 

chemical composition of soils and their subsoils, as given 
in the table, pages 84-87, it will be seen that the 
insoluble residue, lime, phosphoric acid, and manganese 
are more abundant in the surface soil, while in the sub- 
soils the soluble silica, peroxide of iron, and alumina 
appear in highest percentages, while the other ingredi- 
ents are sometimes more abundant in one and sometimes 
in the other. 

If these soils were examined with reference to the sizes 
of the grains composing them, it would be found that in 
the subsoil the small particles, especially in humid 
regions, are most abundant, and hence that the internal 
surface area is much larger in the lower than in the 
upper layers, which may in part explain the higher per- 
centages of soluble ingredients shown by chemical 
analysis. 

Referring again to the table for a comparison of soils 
of humid with those of arid regions, it will be observed 
that these are in some respects quite strongly contrasted 
as regards their chemical composition. The averages 
there given are those of Hilgard, and for the humid 
regions are made up of 466 analyses, while those for the 
arid are a mean of 313 determinations. 

It may be noted in the first place that, excepting the 
insoluble residue, brown oxide of manganese and sulfuric 
acid, all other ingredients are more abundant in the soils 
of arid lands; and not only this, but these differences 
are really large, the amounts being often more than 
double, and in some cases much higher than this. It 
should be said, however, regarding the analyses entering 
into these averages, that all of them come from states 
south of the Ohio River or west of the Missouri, and for 
this reason more fairly represent differences between 



Chemical Composition of Soils. 93 

soils of unglaciated areas in humid and arid regions 
than of soils in general. It appears, too, that many 
of the differences between the soils of the two regions 
largely represented are made more striking than they 
should be through the admission of a relatively larger 
proportion of sandy soils and light loams than of those 
of heavier type, and this will be rendered apparent 
on comparing the soils of the arid regions with the 
ten heavy clay soils in the same table, and still more 
so when the clay subsoils are compared with them. 
The position would seem to be more fully justified, 
too, when it is observed that the analyses of the ten 
sandy soils given in the table approach more nearly 
to the mean of the 466 for humid regions than do 
those of the clay soils ; and also when it is observed that 
the brown oxide of manganese, which is more abundant 
in humid than in arid soils, appears also to be more 
abundant in the sandy than in the clay soils. 

But when all allowances have been made, there are 
still outstanding differences between the soils, formed 
under these widely contrasted climatic conditions, which 
are sharply marked and beyond question. 

In the first place, the insoluble residue is evidently 
more abundant in humid than in arid soils, the ratios 
being in round numbers, as 84 to 70, and this difference 
is held to be due to the much greater amount of leach- 
ing which necessarily takes place where rains fall fre- 
quently and in large quantities. 

The soluble silica, too, an ingredient characteristic of 
the analyses of only heavy soils in humid regions, is 
very abundant in those of arid regions, but the anoma- 
lous feature regarding this is that in its combinations 
in the soil it has not the power of imparting to these 



94 The Soil. 

soils the adhesive plastic quality so characteristic of 
clay lands in humid regions. Whether the soluble 
silica is, in the soil, united largely with alumina to form 
kaolinite or true clay, or whether it is combined to form 
varieties of zeolites, which may be lacking in power to 
give adhesiveness to soil, is unknown. 

Hilgard regards the large percentage of lime, with its 
allied compound, magnesia, as one of the most distinc- 
tive features of the soil of arid regions, and to this lime 
he attributes a flocculation or granulation of the clay, 
which destroys its adhesive quality. To the very gen- 
eral abundance of lime, too, in these soils, alike on the 
high lands and on the low, he attributes the high and 
very uniform productiveness of all these soils whenever 
an abundance of water is supplied to them. 

It seems plain that the high percentages of soluble 
ingredients in the soil of arid regions result from the 
slow decomposition of soil grains brought about by the 
conjoint action of the scanty water which does fall and 
the carbonic acid of the air. Water enough falls for the 
decomposition of rock and the formation of alkalies and 
zeolitic minerals, but not enough to remove them when 
formed, as is the case in humid regions. 

The humus of soils, so far as its chemical composition 
is concerned, is not well understood, neither have we 
attained a satisfactory knowledge of its functions or 
importance as a food for plants. It used to be held that 
any soil deficient in humus was, because of this shortage, 
necessarily poor or sterile, but it is now known that in 
arid regions, where humus in the soil is very scanty or 
even wanting, large crops are produced when only an 
abundance of water is supplied. Experiments in water 
culture, too, have proved that when nitrogen is supplied 



Chemical Composition of Soils. 95 

to plants in the form of purely inorganic or mineral 
nitrates, plants will thrive in the complete absence of 
humus. 

Humus is derived from the partial decay in the soil of 
organic matter, whether that be vegetable or animal, and 
it imparts to the soil a black or brown color. From 
what has been said regarding nature's method of running 
in cycles, it will be readily understood that humus is 
simply the abandoned tissues out of which life has 
moved and which are falling back by degrees into the 
carbonic acid, water, free nitrogen, and ashes out of which 
life reared its marvelous structures. In tropical regions, 
where the soil is warm the whole year through, and in 
arid regions, where the soil is open and readily pene- 
trated by the air, the rate of decay is so rapid that the 
amount of humus found in any soil at any particular 
time is relatively small; but in the temperate climates, 
where the soil is damp and where the ground is too cold 
to permit of decay during considerable portions of the 
year, there the decaying organic matter accumulates in 
considerable quantities and especially on wet soils and 
in swampy places. Beds of peat and the black muck 
soils are the best examples of what is meant by humus, 
and it is excessively abundant in these places because 
the soil is close in texture and so full of water that the 
microscopic forms of life which feed upon this dead 
matter are unable to get the necessary oxygen to thrive 
in it. We should think of humus as the food of micro- 
scopic life in the soil, and of the waste products of this 
microscopic life as a very essential part of the food of 
higher plants. Keeping this in mind, we can better 
appreciate the importance of farmyard manure, for 
through its decay humus is formed. Both are organic 



96 The Soil. 

matter partially decayed and capable of contributing 
food to plants. 

But Hilgard and Jaffa have made the important 
announcement that the humus of arid regions is much 
richer in nitrogen than is that of humid regions, or of 
the humid soils of arid regions. The results of their 
observations, as reported in Agricultural Science for 1894, 
are summarized below : — 

Nitrogen Httmio Nitrogen 





No. 

Samples. 


Humus in Soil. 
Per Cent. 


in Humus. 
Per Cent. 


in Soil. 
Per Cent. 


Arid soils . . 


18 


.75 


15.87 


.101 


Semi-arid soils . 


8 


.99 


10.03 


.102 


Humid soils 


8 


3.04 


5.24 


.132 



In speaking of these results, they say, "It thus 
appears that, on the average, the humus of the arid soils 
contains three times as much nitrogen as that of the 
humid, that in the extreme cases the nitrogen percen- 
tage in the arid humus actually exceeds that of the albu- 
minoid group, the flesh-forming substances." 

" It thus becomes intelligible that in the arid region a 
humus percentage, which, under humid conditions, would 
justly be considered entirely inadequate for the success 
of normal crops, may, nevertheless, suffice even for the 
more exacting crops. This is more closely seen on 
inspection of the figures in the third column, which 
represent the product resulting from the multiplication 
of the humus percentage of the soil into the nitrogen of 
the humus. " 

FUNCTIONS OF THE SOIL INGREDIENTS. 

When we come to speak of the functions or impor- 
tance of the different soil ingredients in vegetable life, 



Functions of the Soil Ingredients. 97 

it must be said that our knowledge is as yet very limited 
and very indefinite. That plants cannot thrive in a soil 
destitute of nitrogen, potash, lime, magnesia, and phos- 
phoric acid has been proved in the most complete and 
satisfactory manner. A soil entirely lacking in any one 
of these is, for that reason, an infertile one. 

Since sulfuric acid, in some of its combinations in the 
soil, is the only known source of sulfur in plants, and 
since sulfur is an essential element in the molecular con- 
stitution of vegetable albumen and allied compounds, it 
follows that fertile soils should always contain an ade- 
quate percentage of sulfates in some form available to 
plants. It will be seen, however, from the table of 
chemical composition, that the amount present in any 
soil, at any time, is usually relatively small. 

Silica, although the most abundant of all the soil 
ingredients, and although present in the tissues of nearly 
all plants, in greater or less amounts, has not been 
demonstrated to have any important part to play in 
plant growth. Indeed, recorded observations go to show 
that plants get along perfectly well when grown in 
media nearly or entirely devoid of this substance. It 
has been supposed that it played an important part in 
giving the necessary stiffness to the stems of cereals, but 
Arendt has shown that the distribution of silica in dif- 
ferent parts of the oat plant is as follows : — 

Lower part of stem 1.7 parts in 1000 of dry substance. 
Middle " " " 5.1 " " 1000 " " " 

Upper " " » 13.3 " " 1000 " " " 

Lower leaves 35.2 " " 1000 " " " 

Upper leaves 43.8 " " 1000 " " " 

Now if the silica were needed for stiffness, the largest 
amounts should be found in the lower and middle por- 

H 



98 The Soil. 

tions of the stem, and more in the stalk than in the 
leaves, while the reverse distribution is observed. 
Indeed, the distribution of silica in the oat makes it 
appear that its presence there is due simply to the fact 
that it was present in the water which passed through 
the plant, and that it was left where the largest amounts 
of evaporation had taken place ; that is, in the leaves and 
in the higher portions of the stem where the wind cur- 
rents are strongest. 

A sufficient amount of an iron salt in the sap of a 
plant appears to be essential to the development of the 
green color of foliage, and without the green chlorophyll 
carbon cannot be assimilated from the carbon dioxide of 
the air. Sachs found, that while young plants of Indian 
corn, when growing in solutions free from iron, had 
their first three or four leaves green as usual, the next, 
and those which followed, were first white at the base 
and green at the tips and afterwards completely white; 
but on adding a few drops of sulfate or chloride of iron 
to the medium in which the plants were growing, the 
green color began to be developed appreciably in twenty- 
four hours, while the normal color was restored in three 
or four days. It is plain, therefore, that iron is a very 
important soil ingredient, although its universal presence 
in the soil, and the small amount of it needed, makes it 
unnecessary to pay any heed to it as a plant food which 
should be supplied as a fertilizer under natural field 
conditions. 

In the movements which result in the transfer of the 
starch-forming products from the green parts of plants 
to their place in the seed, root, or tuber, potash, mag- 
nesia, and lime appear to play an important part, but it 
seems also that before the starch-forming products can 



Kinds of Soils. 99 

be moved a small amount of chlorine must also be pres- 
ent. The amount of chlorine, however, may be very 
small, and as it does not tend to accumulate in the 
places where the starch is stored, it would appear that, 
like the iron, it may be used over and over again. 

KINDS OF SOILS. 

In the language of practical men soils are variously 
classified. They are sometimes spoken of as light or 
heavy, but these terms do not refer to their weight in 
pounds per cubic foot; for those which are called the 
lightest are the heaviest soils we have. A heavy clay soil, 
when dry, weighs only from 70 to 80 pounds per cubic 
foot, while the lightest sandy soils have a weight of 105 
to 110 pounds for the same volume. It is the ease or the 
difficulty with which the soils are worked or tilled 
which gives rise to the terms, light and heavy. In the 
light soils the roots of plants have less difficulty in 
threading their way than in those which are stiff and 
not easily crowded to one side, and as a result of this 
freedom to movement plants distribute their roots much 
more symmetrically and occupy the whole soil more 
completely in the lighter types than they are able to do 
in the stiff and heavy ones. As a consequence of this 
equitable distribution, no root trespasses upon the feed- 
ing ground of another, and the whole soil is laid under 
tribute with correspondingly better returns, when other 
conditions are equally favorable. 

Then, again, soils are spoken of as warm or cold, hav- 
ing reference to their relative temperatures, especially 
during the early part of the season. And here the 
strongest factor in determining the temperature of a 



100 The Soil 

soil is the amount of water it can hold and bring to the 
surface for evaporation, those holding the most water 
and delivering it most rapidly at the surface being usu- 
ally the coldest, and why this is so will be explained in 
another place. 

Soils are sandy when not more than 40 to 65 per cent 
of their weight is made up of particles so small that from 
1000 to 400,000 of them must be placed in line to span a 
linear inch, while the balance may be so large that only 
20 to 100 of them are needed to stretch across the same 
distance. The heaviest clay soils, on the other hand, 
may have 80 to 95 per cent of their weights made up of 
the smallest sizes of particles named above, while only 
5 to 20 per cent of grains of the larger diameters are 
found among them. Loamy soils are such as have their 
grains intermediate between those of the sandy and heavy 
clay types; while between this medium soil we have on 
the coarser-grained side, sandy loams and loamy sands, 
and on the finer-grained side, clayey loams and loamy 
clays, there being, of course, an insensible shading of 
one of these types of # soil into another. 

It has long been observed that these different types 
of soils in all parts of the world are regularly inhabited 
by kinds of plants peculiar to each, and by referring to 
the descriptions of soils on pages 82 and 83, it will be 
seen how sharply contrasted the types of vegetation are 
in that particular region. In the battle of the forests, 
in the race for sunshine and for moisture to meet the 
needs of thirsty leaves, some plants have suited their 
ropts to the coarser and dryer soils, so that they feed 
themselves here more economically than others can; 
while other plants and other trees, in the long years of 
fitting and refitting, have come to thrive better than 



The Store of Plant Food. 



101 



their competitors on the heavy clay soils. Nature, in 
her system of evolution, has developed a division of 
labor among plants just as she has among animals. 
She saw, long ago, that in order that sunshine might 
bring the largest returns out of soil, air, and water, 
there must be special adaptations to a limited set of 
conditions, and just as woodpeckers are a family of 
birds peculiarly fitted to gleaning food from the trunks 
of trees, so there are plants peculiarly adapted to the dif- 
ferent types of soil. 

Besides the soils just referred to there are the swamp, 
muck, peat or humus soils, which contain a very high per 
cent of decaying organic matter or humus, before referred 
to but these only occur in wet, undrained localities. 



THE STORE OF PLANT FOOD. 

Let us look now to the relation between the amount 
and kinds of mineral food materials stored in the soil 
and that removed by crops. Professor Wolff gives the 
composition of some fresh, or air-dry, agricultural prod- 
ucts as follows : — 





Maize. 


Oats. 


Winter 
Wheat. 


Winter 
Eye. 


Barley. 


Eed 
Clover. 




Is 

t/2 


.5 

u 

o 


13 


a 

o 


M 

*c5 


a 

'rt 
u 

O 


M 

ZO 

40.7 


H 

U 






"3 


O 


Total ash . . . 


47.2 


12.3 


44.0 


26.4 


42.6 


17.7 


17.3 


43.9 


21.8 


56.5 


36.9 


Potash . . . 


16.6 


3.3 


9.7 


4.2 


4.9 


5.5 


7.6 


5.4 


9.3 


4.8 


19.5 


13.8 


Soda .... 


0.5 


0.2 


2.3 


1.0 


1.2 


0.6 


1.3 


0.3 


2.0 


0.6 


0.9 


0.2 


Magnesia . . . 


2.6 


1.8 


1.8 


1.8 


1.1 


2.2 


1.3 


1.9 


1.1 


1.8 


6.9 


4.5 


Lime . . ^ . 


5.0 


0.3 


3.6 


1.0 


2.6 


0.6 


3.1 


0.5 


3.3 


0.5 


19.2 


2.3 


Phosphoric acid 


3.8 


5.5 


1.8 


5.5 


2.3 


8.2 


1.9 


8.2 


1.9 


7.2 


5.6 


12.4 


Sulfuric acid 


2.5 


0.1 


1.5 


0.4 


1.2 


0.4 


0.8 


0.4 


1.6 


0.5 


1.7* 


1.7 


Silica .... 


17.9 


0.3 


21.2 


12.3 


28.2 


0.3 


23.7 


0.3 


23.6 


5.9 


1.5 


0.9 


Sulfur .... 


3.9 


1.2 


1.7 


1.7 


1.6 


1.5 


0.9 


1.7 


1.3 


1.4 


2.1 





102 



The Soil 



From this table it appears that each 1000 pounds of air- 
dry product requires from the soil the number of pounds 
of each ingredient there indicated. Taking clover as an 
illustration, each ton of clover hay demands for its pro- 
duction 39 pounds of potash, 1.8 pounds of soda, 13.8 
pounds of magnesia, 38.4 pounds of lime, 11.2 pounds of 
phosphoric acid, and 3.4 pounds of sulfuric acid ; and two 
tons of hay per acre makes the annual demand double 
these amounts. What has the soil to offer ? 

If we take the mean dry weight of a surface foot of 
soil at 80 pounds and the mean soluble ingredients of soils 
at the percentages given by Hilgard on pages 84-87, 
regarding these as indicating the available plant food, 
then the amounts in the surface foot of an acre of land 
may be shown to be as follows : — 



Potash 
Soda 
Magnesia 
Lime 

Phosphoric acid 
Sulfuric acid 
Soluble silica 



in surface foot, per acre 





. 3.76 tons 


. . 1.58 " 






3.92 ' 






1.88 ' 






. 1.97 ' 






.91 ' 






. 73.40 ' 








It is not unfair to assume that every young man who 
starts on a farm of his own may be interested in its main- 
tenance for 50 years on his own account and for 50 more 
years for the sake of his children. What then are the 
demands on the soil for 100 years likely to be ? To 
give defmiten£ss and simplicity rather than exactness to 
our problem, let us assume that a three-year rotation of 
corn, clover, and oats shall be adhered to throughout; 
that the clover shall all be cut as hay and with the straw 
and corn stalks, or their equivalents, constitute a revolv- 
ing fund, never to go permanently off the farm ; while 



The Store of Plant Food. 



103 



the equivalent of the grain in some form shall be sold 
and no part returned to the land. Assume, further, that 
each and every year the yields shall be exactly two tons 
per acre of air-dry product, and that in the case of the 
corn and oats one-half of the product shall be grain and 
the other stalks or straw. Under these conditions how 
long will the several credits — potash, soda, magnesia, 
lime, phosphoric acid, sulfuric acid, and silica — last ? 

On the basis of these assumptions the amounts of the 
several ash ingredients required to be extracted from the 
soil by each of the three crops during the 33 years out of 
99 which it will have fed upon the ground would be, — 

FOR THE REVOLVING FUND. 





Pot- 
ash. 


Soda. 


Mag- 
nesia. 


Lime. 


Phos- 
phoric 
Acid. 


Sulfur 

as Sul- 
furic 
Acid. 


Silica. 




lbs. 


lbs. 


lbs. 


lbs. 


lbs. 


lbs. 


lbs. 


Clover .... 
Oat straw . . . 
Corn stalks . . 


2571.0 

640.0 

1095.5 


118.8 

151.8 

33.0 


910.8 
118.8 
179.7 


2534.0 
237.6 
330.0 


739.2 
118.8 
250.8 


536.5 
442.6 
953.0 


198.0 
1399.0 
1181.5 


Total in 100 yrs. 


4309.5 


303.6 


1209.3 


3101.6 


1108.8 


1932.1 


2778.5 



FOR THE EQUIVALENT OF GRAIN SOLD. 



Oats .... 


277.2 


13.2 
66.0 


118.8 
118.8 


19.8 
66.0 


363.0 
363.1 


249.2 
370.0 


19.8 
812.0 


Total in 


100 yrs. 


495.0 


79.2 


237.6 


85.8 


726.1 


619.2 


831.8 



If we now divide the amounts of the several ash 
ingredients which chemical analysis points out as exist- 
ing in the surface foot of the average soil of the humid 
regions, included in Hilgard's studies, by the amounts of 



104 The Soil 

these ingredients supposed to be sold and hence removed 
permanently from the land, the results will indicate the 
number of years required for the removal of the amount 
of the several ash ingredients standing to the credit of 
the surface foot of soil at the beginning of the 100 years. 
Making these divisions we get, 

Potash enough to last 1521 years. 



Soda 


t< L 


4050 


Magnesia 


K i 


3300 


Lime 


U ( 


4387 


Phosphoric acid 


a t 


542 


Sulfuric acid 


a i 


292 


Soluble silica 


u ; 


' 17650 



When it is observed that cultivated plants send their 
roots foraging through not less than the upper four feet 
of soil, and that the amounts of ash ingredients which 
have been considered are only those which chemical 
analysis tells us are to be found in the surface foot, it 
seems well-nigh impossible that there could ever be a 
deficiency in any one of the ash ingredients which plants 
find essential to their well-being. 

Notwithstanding the apparently inexhaustible stores 
of potash, magnesia, lime, phosphoric acid, etc., in the 
soil, it must be remembered that we are nevertheless con- 
fronted with the indisputable results of practical field 
work which show, very often at least, that the addition 
of purely mineral fertilizers have been associated with 
larger yields per acre. We are confronted on every 
hand, too, with the fact that lands do run out and 
some varieties much more quickly than others ; so that, 
when all has been said, the most important fact to 
bear in mind is that here is a problem lying at the very 



The Store of Plant Food. 105 

foundations of agriculture upon which a vast work has 
yet to be done. 

In support of this view let me place in evidence some 
of the results obtained by Sir J. B. Lawes and his associ- 
ates during their classic experiments bearing upon the 
conditions which determine the fertility of soils. By 
growing various crops year after year on the same land, 
to which no nitrogen-bearing manures were applied, they 
found that when purely mineral fertilizers were added, 
the crops were able to produce larger yields and to extract 
more nitrogen from the soil than when these fertilizers 
were omitted. Wheat, for example, grown continuously 
on the same land for 32 years without manures of any 
kind, was able to extract from the soil and build into its 
product 20.7 pounds of nitrogen per acre, per annum, but 
the same crop, on adjacent and similar lands, to which 
mineral fertilizers without nitrogen were added, was able 
to gather and store 22.1 pounds, an amount 6.76 per cent 
larger. Barley, during 24 consecutive years, drew from 
the soil 18.3 pounds of nitrogen per annum, where no 
mineral fertilizers were added, but 22.4 pounds per acre 
under the stimulus from them. Beans gathered from 
their land 31.3 pounds of nitrogen per acre where no 
fertilizer was added, as an average of 24 years, but 45.5 
pounds where complex mineral food was given them. 
Ground bearing 6 crops of clover in 22 years, with 1 
of wheat, 3 of barley, and 12 years fallow ground, gave, 
without fertilizers, 30.5 pounds of nitrogen per acre, but 
with the mineral fertilizers, 39.8 pounds. So, too, in a 
rotation of crops, 7 courses in 28 years, no fertilizers, gave 
36.8 pounds, while with superphosphate of lime the 
yield was 45.2 pounds per acre. Then, again, in the mixed 
herbage of grass land, 20 years without fertilizers gave a 



106 The Soil * ■ 

mean yield of 33 pounds, but with a mixed mineral fer- 
tilizer, containing potash, the product of nitrogeu was 
55.6 pounds per acre, per annum. 

Such results as these place beyond question the fact 
that, in spite of the large stores in the soil of all the ash 
ingredients used by plants, the addition of mineral salts 
more or less closely allied to those found there do give to 
the plant an added power over the natural resources of 
the soil in which they may be growing ; and the marvel- 
ous part of the whole problem is that so small an amount 
of the fertilizer, when diluted by so much soil and water, 
can exert the appreciable effects observed. 






CHAPTER III. 

NITROGEN OF THE SOIL. 

In speaking of the chemical composition of the soil, 
very little has thus far been said regarding nitrogen, the 
most important, perhaps, of all the ingredients ; and for 
the reason that the loss of it from the soil is so rapid 
under faulty management, and the demands for it so 
urgent, as to claim for its consideration a separate 
chapter. 

THE STORE OF SOIL NITROGEN. 

We have seen that the total amount of the ash ingredi- 
ents of plant food stored in the surface four feet of soil 
is very large, and so, too, is the total nitrogen, when con- 
sidered in all its combinations. Storer, citing the obser- 
vations of Krocker, to the effect that cultivated soils rarely 
contain less than .1 per cent of nitrogen, calculates the 
amount stored in the surface foot as seldom less than 
3500 pounds per acre. This is an amount so large that if 
Ave take Warington's estimate of the nitrogen removed 
from the soil by wheat, when producing 30 bushel per 
acre, there is enough for more than 70 such crops, count- 
ing 33 pounds of nitrogen in the grain and 15 pounds in 
the straw. The mean amount of nitrogen in eleven ara- 
ble and grass soils at Rothamsted is placed by Lawes and 
Gilbert at .149 per cent, and for eight other Great Britain 

107 



108 



The Soil. 



soils at .166 per cent. Four Illinois prairie soils were 
shown by Voelcker to contain .308 per cent; while 
seven rich Russian soils have been shown by C. Schmidt 
to contain .341 per cent of nitrogen. If we bring all of 
these thirty analyses together into one mean, we shall 
have .219 per cent, an amount more than double that 
used by Storer as stated above. 

In studying the fertility of the rich prairie soils of 
Manitoba, Lawes and Gilbert found that the surface foot, 
from four different localities, contained an average of .373 
per cent of nitrogen, or enough, could it all be utilized in 
wheat production, for some 6500 bushels from each and 
every acre of land. 

But the nitrogen of these and other soils is not all con- 
tained in the surface foot, and the distribution of it in the 
surface four feet of the soils in question, as they learned 
through chemical analysis, is given in the table below, 
which shows that the total amount is more than as large 
again as that given for the surface foot. 

AMOUNT OF NITROGEN PER ACRE IN SURFACE FOUR FEET 
OF FOUR MANITOBA SOILS. 



Depth. 
1st foot 
2d foot 
3d foot 
4th foot 

Total 



VERVILLE. 

lbs. 


Brandon. 
lbs. 


Selkirk. 

lbs. 


Winnipeg 
lbs. 


7308 


5236 


17304 


11984 


5408 


3488 


8448 


10464 


2484 


2502 


2736 


5688 


1520 


870 


1487 


4045 



16720 



12186 29975 32181 



Nor can it be urged with these soils that the nitrogen 
is in a form which cannot, under favorable conditions 
of tillage, be converted into nitric acid and nitrates, the 
form in which nitrogen is largely used by cultivated 



The Store of Soil Nitrogen. 109 

plants ; for Sir J. B. Lawes caused samples of these soils 
to be placed under favorable conditions for nitrification, 
where they were held, with some interruptions, during 
something more than 300 days and during this time it is 
estimated that not less than 799.8 pounds per acre, as an 
average for the four soils, were converted into soluble 
nitrates available for crop production, as shown in the 
table which follows : — 

AMOUNT OF NITROGEN PER ACRE CONVERTED INTO 
SOLUBLE FORM. 



Depth. 


Mean Per Cent 
of Total 
Nitrogen. 


Niyerville. 

lbs. 


Brandon. 

lbs. 


Selkirk. 
lbs. 


Winnipeg 

lbs. 


1st foot 


4.295 


234.1 


250.4 


655.1 


650.0 


2d foot 


2.733 


72.9 


57.2 


377.5 


372.5 


3d foot 


2,108 


12.6 


53.7 


27.2 


276.0 


4th foot 


L443 


15.0 


10.7 


11.5 


112.8 



Total 334.6 372.0 1071.3 1411.3 

While the conditions under which these samples were 
placed for nitrification were much more favorable for the 
rapid carrying forward of the process than could be pro- 
duced in the natural soil, it should not be inferred that 
the amount so changed represents the total available 
nitrogen in these soils ; for there appears to be no reason 
why time and favorable conditions may not transform 
into soluble nitrates much the larger portion of that 
which the analyses have shown them to contain. 

The presence of these large amounts of nitrogen and 
of ash ingredients which soils have been shown to pos- 
sess are very fundamental facts, which must be kept ever 
in mind in our efforts to restore the vigor of exhausted 
soils and to maintain a high degree of productiveness in 
them when so brought back. They are important because 



110 The Soil 

they show very clearly that run-out lands, and lands tired 
of this crop or of that, have been rendered so by some 
change different from the consumption of the chemical 
ingredients contained in soils out of which plant food is 
elaborated. They are important because they bring 
clearly into view the fact that, as yet, our practices re- 
garding the rotation of crops, regarding the fertilizers or 
manures for this soil or that crop, and regarding many of 
our efforts to improve our lands by this or that method 
of tillage, are all of them far too much like those of a 
man feeling his way in the dark. They are important 
because they show that the agriculture which shall be 
able to feed the crowded cities, so rapidly building, as 
cheaply as they must be fed, must bring to its aid the 
mightiest efforts of the strongest minds, and must place 
the management of its lands under trained men whose 
education is unexcelled in its kind by that of any other 
trade or profession. 

IMPORTANCE OF NITROGEN IN PLANT LIFE. 

Nitrogen, sulfur, and phosphorus are the three elements, 
derived from the soil, which are largely peculiar to those 
highly complex compounds so immediately associated 
with the life processes of plants. It is true that oxygen, 
carbon, and hydrogen, combined to form cellulose, out of 
which the framework of vegetation is built, and to form 
the starches, sugars, and gums, make up by far the larg- 
est part of the dry weight of vegetable matter ; but these 
appear to be only products which have resulted from the 
transformations which take place within the protoplas- 
mic substance of which nitrogen, sulfur, and, at times, 
phosphorus appear to be the controlling or life-leading 



Importance of Nitrogen in Plant Life. Ill 

elements. While carbon, oxygen, and hydrogen make 
np the larger part by weight of these responsive sub- 
stances, yet by themselves they build into molecules too 
strong and too stable to be again thrown down by sun- 
shine alone. Like the stick, which constitutes both the 
bulk and the chief source of heat in the common match, 
but a useless thing with which to kindle a fire unless 
tipped with the easily upset molecules of phosphorus, sul- 
fur and nitre, which by their fall produce the necessary 
heat to fire the bit of wood, so the starches, the gums, 
and the fats stored in the seeds, in the fleshy roots and 
thickened steins and leaves of plants, could not serve as 
food and become sources of power, either in plants or in 
animals, were there not associated with them enough of 
those proteid or albuminoid molecules containing nitro- 
gen, sulfur, and perhaps also phosphorus which, after 
absorbing a little too much water, are easily overturned 
by the warmth of the soil, and thus in their fall set on 
foot the train of changes it is their mission to start and 
to maintain. 

It is very suggestive and not a little strange, in this 
connection, that one of the most powerful explosives we 
have is now made by slipping out of cellulose three of 
its hydrogen atoms and placing in their stead three 
groups of two atoms taken from nitric acid, this result 
being accomplished by simply steeping cotton wool in 
strong nitric acid, made more active by mixing with it 
twice its volume of concentrated sulfuric acid. When 
this is done and the wool has been washed and dried, it 
is found that, without having lost even its fibrous struc- 
ture, the taking-out and slipping-in process has resulted 
in so unsteady a structure that a trifling disturbance 
causes it to fall apart with explosive violence. So, 



112 The Soil. 

too, when glycerine is treated in a similar manner, a 
slipping-out and slipping-in change takes place ; three 
bricks, so to speak, — three atoms of hydrogen, — are 
replaced by three others derived from the nitric acid, 
and instead of the oily, sweetish liquid, glycerine, we 
have the fearful nitroglycerine which, when mixed with 
earth, constitutes dynamite. Even in our old explosive, 
gunpowder, we employ the same nitric acid in combina- 
tion with potash as saltpetre, which, with the addition of 
a trifling amount of heat, is made to give over its oxygen 
to the carbon and sulfur with which it is mixed, and, 
by uniting with them, almost instantaneously develops 
the power sought. 

Now Ave are not trying to point out here just how the 
energy manifested in the tissues of plants and in the 
bodies of animals is derived: we are rather trying to 
point out how indispensable to the life of plants nitro- 
gen is, that we may the more fully feel the urgency of 
holding its amount and condition in the soils we till up 
to the standard demanded by vigorous plant growth. 
All are agreed that, varied as the constructive and de- 
structive processes of plant life are, they take place 
within or are directly or indirectly set up by, the molecu- 
lar shif tings, adjustments, and readjustments within the 
protoplasmic substance of cell life, of which nitrogen is 
an indispensable ingredient. 

RELATION OF SOIL NITROGEN TO CROP DEMANDS. 

Just how is the amount of nitrogen removed by a 
crop from the soil related quantitively to the ash ingre- 
dients, and how are the amounts of these in the soil 
related to the several amounts in the crop ? The crop 



Relation of Soil Nitrogen to Crop Demands. 113 

of wheat which yields 30 bushels of grain per acre 
demands, as indicated by chemical analysis, 48 pounds 
of nitrogen, 21.1 pounds of phosphoric acid, 28.8 pounds 
of potash, 9.2 pounds of lime, 7.1 of magnesia, 7.8 of 
sulfur, and 96.9 pounds of silica. A crop of oats yield- 
ing 60 bushels per acre would demand: of nitrogen, 73.3 
pounds; phosphoric acid, 25.7 pounds; potash, 61.5 
pounds ; lime, 15 pounds ; magnesia, 11.6 pounds ; sulfur, 
10.7 pounds ; and of silica, 113.7 pounds. In the case of 
red clover, yielding 2 tons of hay per acre, the demands 
are : for nitrogen, 102 pounds ; phosphoric acid, 24.9 
pounds ; potash, 83.4 pounds ; lime, 90.1 pounds ; mag- 
nesia, 28.2 pounds ; sulfur, 9.4 pounds ; and silica, 7 
pounds. These are the amounts of plant food, of the 
kinds named, demanded from each acre of ground in the 
cases cited. 

Taking the average per cent of nitrogen in the surface 
foot of soil at .15 per cent, the weight of the soil at 80 
pounds per cubic foot, and the ash ingredients as indi- 
cated on page 101, it will be seen, after dividing the 
amounts of the several ingredients in the soil by the 
respective amounts demanded in the three cases, that, 
could the materials be all used, there would be of 







Wheat. 


Oats. 


Clover 






Crops. 


Crops. 


Crops. 


Nitrogen, 




enough for 109 


72 


52 


Phosphoric 


acid, 


« 187 


153 


158 


Potash, 




" " 261 


122 


90 


Lime, 




" " 409 


251 


42 


Magnesia, 




" « 1104 


676 


278 


Sulfur, 




« - 76 


56 


63 


Soluble silica, 


" " 1515 


1291 


20970 



In these figures it is assumed that nothing is given 



114 The Soil. 

back to the soil by the crops, which, however, is not 
true regarding nitrogen, especially with the clover. It 
will be seen from the figures that the supply of nitrogen 
is relatively less than that of any other ingredient except 
sulfur. 

If it were true that all of these plant foods are both 
equally available and necessary, and the possibilities of 
loss the same, then the tendency would be for the nitro- 
gen and sulfur to give out earliest. Now, in the case 
of nitrogen, certainly no plant food from the soil is 
more important and probably no one is subject to as 
great loss under bad management as this ; and hence it 
follows that much attention should be paid to this soil 
ingredient. 

FORMS OF NITROGEN IN THE SOIL. 

Nitrogen occurs in the soil under several different con- 
ditions, and is derived from several sources. As a part 
of the soil air, it exists as free nitrogen where it is es- 
sential to the life of certain microscopic forms which 
seize upon it and render it available to higher plants. 
Temporarily and in transition stages, nitrogen occurs in 
the soil as ammonia and as nitrous acid, but these forms 
pass rapidly, apparently, into nitric acid, from which 
most of the higher plants derive their chief supply. 
* The amount, therefore, of ammonia or of nitrous acid 
existing in a soil at any time is always small. In the 
form of nitric acid, however, the soil contains con- 
siderable amounts of nitrogen, as nitrates of lime or 
other bases, but in this form Warington states that 
the amount seldom reaches 5 per cent of the total nitro- 
gen content. 



Distribution of Nitrogen in the Soil. 115 

By far the larger part of the nitrogen of soils is stored 
in the form of humus, to which reference has already 
been made ; and this, through the processes of fermen- 
tation, is gradually made available to plants in the form 
of nitric acid. The roots of field crops, too, contribute 
no small amount of material to the store of organic mat- 
ter in the soil, a part of which is converted into humus ; 
but the plants whose roots leave in the soil the largest 
amounts of nitrogen are the leguminous species, like the 
clovers, beans, peas, and lupines. 



DISTRIBUTION OF NITROGEN IN THE SOIL. 

Regarding the distribution of nitrogen in the soil, some 
facts have already been given on page 108. Referring to 
the table, it will be seen that the amount decreases down- 
ward until in the fourth foot the average is less than 
one-fifth of that found in the first foot. This decrease 
in the amount of nitrogen is evidently due in part to the 
variation in the distribution of roots in the soil, and 
perhaps largely to this cause ; but there are other factors 
which tend sometimes to cause a destruction of the nitric 
acid, setting free the nitrogen in the gaseous form. Ob- 
servation has shown that when a soil rich in nitrates is 
saturated with water so as to exclude free oxygen, a 
deoxi elation may take place which sets free nitrogen gas ; 
nor is this action limited to the nitrates, for organic mat- 
ter is also broken down under these conditions, with a 
setting free of both carbon dioxide and nitrogen gas. 

The distribution of nitrogen in Rothamsted soils is 
given by Warington to a depth of 9 feet, and the results 
are quoted as follows : — 



116 



The Soil. 



NITROGEN IN SOILS AT VARIOUS DEPTHS. 





Arable Soils. 


Old Pasture 

Soils. 




lbs. per acre. 


lbs. per acre. 


First 9 inches contained 


3015 


5351 


Second 9 " " 


1629 


2313 


Third 9 " " . 


1461 


1580 


Fourth 9 ' l " 


1228 


1412 


Surface 3 feet contained . 


7333 


10656 


Fifth 9 inches contained 


1090 


1301 


Sixth 9 " " 


1131 


1186 


Seventh 9" 


1049 




Eighth 9 " " 


1095 




Second 3 feet contained . 


4365 




Ninth 9 inches contained . 


1173 




Tenth 9 " 


1076 


. 


Eleventh 9 inches ' ' 


1112 




Twelfth 9 " " 


1198 




Third 3 feet contained . 


4559 




Surface 9 feet contained 


16257 








It will be seen from this table that the amount of 
nitrogen in an old arable soil may be really very large, 
in this case enough, could it all be used, for 338 crops 
of wheat of 30 bushels per acre, or more than 10,000 
bushels. It will be seen also that, after the first three 
feet are past, the total amount of nitrogen in the suc- 
ceeding feet remains nearly constant, or that it tends 
very slightly to increase. The figures suggest that at a 
certain depth below the surface of arable fields, the 
amount of nitrogen tends to remain approximately con- 
stant from year to year, while the rise and fall of this 
ingredient is a phenomenon largely peculiar to the surface 
three or four feet. 



Sources of Soil Nitrogen. 117 

Referring now to the distribution in the soil of the 
nitrates simply, it must be said that the amounts of these 
found at different depths varies with the season and to 
some extent also with the crop. At the time crops are 
growing, the roots remove the nitrates, where these roots 
are found, so thoroughly that the measured amount at 
any one place is small, the plants tending to pick it up 
as rapidly as it may be formed. At the end of a season, 
when percolation has been taking place for some time, 
the nitrates are largely removed in the drainage waters, 
or they are carried far below the surface. So too, if a 
considerable quantity of nitrates have newly formed near 
the surface and there comes a heavy rain which produces 
percolation from the first foot into the second foot of 
soil, the effect of this percolation is to shove along in its 
front layer of moving water nearly all of the readily 
soluble salts the soil may have contained, thus changing 
their position from the first to the second foot in perhaps 
one or two days. Such action as this tends to concen- 
trate the nitrates in a thin zone and at times possibly 
wholly below the territory occupied by the roots. Such 
concentrations, however, cannot be permanent; for both 
diffusion and capillarity tend to bring about a redistribu- 
tion again. 

SOURCES OF SOIL NITROGEN. 

When we ask, From whence comes the nitrogen of the 
soil ? we raise one of the most important questions of 
practical agriculture, and one which is to-day taxing, to 
the utmost, the skill of many very able investigators. 
When the earlier investigators upon this subject found 
their results, one after another and almost without 



118 The Soil. 

exception, pointing to one conclusion, namely, that the 
plants upon which they experimented either did not in- 
crease the total nitrogen given them or where an increase 
appeared to be associated with their growth this was so 
small, or of such a character, that it seemed more than 
likely it might have been derived in some way outside of 
the direct action of the plant under experiment, it came 
to be almost accepted that the vegetable world depended 
for its nitrogen upon the decay of organic substances sup- 
plemented in small part by the nitric acid and ammonia 
which are brought down by the rains and the snows or 
condensed in the dews. It was indeed early observed 
that clover could be grown upon land relatively poor in 
nitrogen, and at the same time remove in the crop pro- 
duced large amounts of that ingredient, while a crop of 
wheat following the clover was able to procure more 
nitrogen from the same field, following the clover, than 
it was able to do before the clover had occupied the land 
and taken from it its large amounts of nitrogen. We 
now know that the growth of clover upon land may be 
associated with the accession from the atmosphere of 
large amounts of nitrogen, but the studies of the earlier 
investigators prevented them from believing such an 
explanation possible, and various hypotheses were ad- 
vanced to explain the advantages derived from systems 
of rotation in which clover was one of the series. 

The fact that nitrates were early known to be drained 
away from the land in large quantities and that nitrogen 
gas is liberated during the processes of decay, when 
coupled with the fact that life has existed upon the land 
during untold geologic ages, should have made it appear 
inevitable that there must be some way for drawing from 
the free nitrogen of the air a supply sufficient to make 



Sources of Soil Nitrogen. 119 

good the losses referred to, and especially when it was 
known that the rocks themselves, from which soil is de- 
rived, do not contain the element in appreciable quan- 
tities. And then whenever the question was asked, 
From whence came the nitrogen which entered into the 
very earliest forms of life and which made the very earliest 
soils fertile ? it should have seemed almost axiomatic 
that the nitrogen of the air must be used over and over 
again, as we now know, but only through the studies of 
the last decade, that it in reality is. 

The amounts of nitrogen brought to the soil in the 
form of nitric acid and ammonia, with the moisture precip- 
itated as rain, snow, and dew, are known to be relatively 
small, rarely more than the equivalent of 5 pounds per 
acre per annum in the open country removed from the in- 
fluence of the burning fuel and products of sewage decom- 
position associated with the life of large cities. A 
knowledge of the actual amounts of nitrogen so derived 
has been gained by keeping records of the total precipita- 
tion and by determining the amounts of nitrogen such 
waters did actually contain. Some of the results which 
were obtained through careful studies at Rothamsted are 
given in the following table : — 

NITROGEN AS AMMONIA AND NITRIC ACID, IN POUNDS 
PER ACRE PER ANNUM, IN RAIN. 

Rothamsted. Lincoln, New Zealand. Barbadoes. 

8 years. 3 years. 3 years. 

lbs. lbs. lbs. 

Nitrogen as ammonia .2.53 0.74 0.93 

Nitrogen as nitric acid .0.84 1.00 2.84 

3.37 1.74 3.77 

These amounts, it will be seen, are only sufficient to 
contribute the necessary nitrogen for about two bushels 



120 



The Soil. 



of wheat per acre where 48 pounds is counted sufficient 
for 30 bushels of wheat. 

Observations similar to the above have been made in 
various parts of Europe, and the mean of 22 determina- 
tions, each extending over a whole year, at nine different 
stations, give results varying from 1.86 pounds of nitro- 
gen per acre to 20.91 pounds, with a mean value of 10.23 
pounds per acre where the average amount of rainfall was 
27.03 inches. From these figures it will be readily seen 
that even were any country to receive annually supplies 
of nitrogen equal to the largest amount here stated, the 
quantity would be insufficient for continuous large crops, 
even could the whole of it be used for that purpose. 

Before leaving this subject, — the contributions of rain 
to the soil, — let us quote a table from Dr. Angus Smith 
in " Air and Rain," in which the average composition of 
rain water from various parts of England and Scotland 
are given. 

AVERAGE COMPOSITION OF SAMPLES OF RAIN IN PARTS 

PER MILLION. 





Nitrogen as 








Ammonia. 


Nitric 
Acid. 


Chlorine. 


Acid. 


England, country places, in- 












.88 


.19 


3.88 


5.52 




4.25 


.22 


8.46 


34.27 


Scotland, country places, 












.61 


.11 


12.24 


5.64 




.44 


.08 


3.28 


2.06 




3.15 


.30 


5.70 


16.50 




7.49 


.63 


8.72 


70.19 



Sources of Soil Nitrogen. 121 

From this table it will be seen the rains bring down 
larger amounts, both of chlorine and of sulfuric acid 
than of nitrogen in both of its combinations. It will be 
observed that in and about towns and cities all of the 
ingredients are more abundant than they are in the open 
country, and that the chlorine, which occurs in the air in 
the form of common salt, is more abundant near the sea 
than it is farther inland, as should be expected because 
it is largely derived from sea-water. The salt does not 
evaporate, but in times of high winds, when the water on 
the crests of the waves and breakers is whipped into fine 
spray, the water so taken into the air is evaporated, leav- 
ing the salt floating in the air as fine particles of dust 
about which the raindrops form and so bring them to 
the ground. Since England and Scotland together form 
a relatively small body of land entirely surrounded by 
salt water, it is probable that both the amounts of salt 
and of sulfuric acid, even from the country places in- 
land, are larger than are likely to be observed in the 
interior of continental areas. The large differences be- 
tween the cities and the country, shown in the table, are 
due chiefly to products of combustion, issuing from the 
many stoves, furnaces, and engines which are concen- 
trated within their borders. 

If we take the average of the sulfuric acid from the 
inland country places in England and Scotland and cal- 
culate the amount of sulfur per acre with different depths 
of rainfall, and then set these amounts alongside of the 
amounts of sulfur which chemical analysis has shown to 
occur in crops of wheat, oats, and clover, as given on page 
101, we shall have the results which follow : — 

With rain containing 3.79 parts of sulfuric acid per 
million, — 



122 The Soil. 

Sulfite. 
12 inches of rain would yield .89 pounds per acre. 

24 " " " n tt ^ 78 4t " " 

30 " " " " " 2.66 tk " " 

30 bushels of wheat demand 7.8 " " " 

60 bushels of oats demand 10.7 " " " 

2 tons of clover hay demand 9.4 " " " 

It appears therefore, from these results, that even with 
36 inches of rain per annum, less than one-third of the 
necessary amount of sulfur needed by large yields of 
crops per acre can be supplied by the sulfuric acid of 
rains. 

It is held by some that gaseous ammonium carbonate 
passing in the air over the foliage of vegetation may be 
absorbed by the leaves, and thus contribute to the supply 
of nitrogen for the purposes of plant growth ; but upon 
this point the evidence appears to be insufficient even to 
place beyond question the fact of such a source of nitro- 
gen, much less to allow of a quantitative expression of 
its amount. 

Schlosing, however, in his experiments on moist soils 
freely exposed to the air, believes he has shown that under 
certain conditions soils may acquire nitrogen, through such 
an exposure, at the rate of 38 pounds per acre per annum, 
and the additions to his experimental soils appear to have 
been largely in the form of ammonia. It will be readily 
understood that if soils do have the power of removing 
from the passing air the compounds of nitrogen it con- 
tains, the amounts of nitrogen added to the soil in the 
combined form might easily be more than that which is 
brought down by the rains, because the steady ongoing of 
the winds across the surface of the land must necessarily 
bring a very large amount of air in contact with a given 



Sources of Soil Nitrogen. 123 

field of soil during the course of any season. Still, to 
obtain 38 pounds of nitrogen from the air in the form of 
ammonia, means the complete removal of this gas from 
a very large volume of air. 

The daily analysis of air on Montsouris from 1876 to 
1881 gave the mean quantity of ammonia in the air at 
2.2 milligrams for each 100 cubic metres, and for a soil to 
acquire 38 pounds of nitrogen from the ammonia, it must 
completely extract from the air that which is contained 
in 951.4 millions of cubic metres. This means that if, 
on an acre, the air one metre deep, which is a little more 
than 3 feet, were to give up all of its ammonia to the 
soil, that air would have to be changed more than 2.5 
million times in order to bring the necessary amount 
of ammonia to the acre to yield 38 pounds of nitrogen. 
These and other considerations make it appear quite 
certain that soils, under average field conditions, can- 
not receive annually the above amount of nitrogen 
in this form from the air, at least outside of tropical 
regions. 

It is well established that electrical discharges in the 
atmosphere cause some of the oxygen of the air to unite 
with nitrogen, giving rise to the nitrous and nitric acids 
which the air is known to contain and which have been 
referred to as being brought down by the rain. But it is 
probable that a part of these combinations with oxygen 
are derived from ammonia through the action of ozone, a 
modified and highly active form of oxygen. This action 
is believed by Warington to be supplemented by the per- 
oxide of hydrogen, and hence that the nitrates brought 
down in the rain do not represent so much nitrogen not 
previously combined, but rather that a portion of these 
may have resulted from the oxidation of ammonia. 



124 The Soil. 



FREE-NITROGEN-FIXING GERMS. 

We come now to consider one of the most important 
discoveries of modern times ; a discovery which places 
in the hands of every farmer a means, completely under 
his control, whereby he can at any time cause to be drawn 
directly from the atmosphere the free nitrogen of the air 
and have it fixed in the soil of any field he may wish to 
enrich. 

The history of this important discovery cannot be given 
here, but in 1888 Hellriegel published the results of his 
experiments, which satisfactorily proved that we have in 
nature great numbers of minute microscopic organisms 
living in the soil, which have the habit of locating them- 
selves upon the roots of certain kinds of plants and 
especially upon the clovers, beans, peas, lupines, and other 
leguminous species. These organisms, once seated upon 
the roots of a plant congenial to them, cause the forma- 
tion of little enlargements or tubercles, in which they 
live, drawing nourishment from the plant upon which 
they have established their home, but in return giving to 
it compounds of nitrogen which these organisms are able 
to produce from the free nitrogen of the soil air. Here 
we have two neighbors changing work ; each performing 
that sort of labor which, through long years of specializa- 
tion, it has become best fitted to do, and then swapping 
the products of their labor to the mutual advantage of 
both. The clover, with its leaves outspread in the free 
air and fitted to utilize the bright sunshine as a source of 
power, breaks down the molecules of carbon dioxide, 
forging them into such compounds as it needs ; but in its 
efforts to utilize to the best advantage all of its surround- 



Free-Nitrogen-Fixing Germs. 125 

ings, it has given over the first rough forging of nitrogen 
into food to the lowly organisms upon its roots, and now 
sends down to them so much of such compounds best 
brought together under the hammer of direct ether waves 
as they need in doing their part of the work. Like the 
coal brought up from the mine, like the fuel in the 
engine, the products made in the green leaf and sent 
down to the lightless cellars become the source of power 
there used by the one-celled plants in bringing into com- 
bination with oxygen the free nitrogen of the air, so 
indispensable to the life of higher plants. What a com- 
munity of life ! What a complete utilization of all forces 
and all materials, both above and below ground, we have 
here ! 

If the roots of clover plants are examined, there may 
easily be seen upon their surfaces many little lumps, 
knobs, or tubercles. Similar bodies may also be observed 
upon the roots of peas, beans, lupines, and other legumi- 
nous plants, and these are the places where colonies 
of the bacteria here under consideration have located 
themselves. These micro-organisms are found scattered 
through the soil, and some believe that they have the 
power, at least certain species, of withdrawing free nitro- 
gen from the air without the aid of another plant on 
which to live, but the matter still awaits positive demon- 
stration. 

Some of Hellriegel's studies make it appear that differ- 
ent species of leguminous plants are inhabited by varie- 
ties of these minute organisms peculiar to themselves. 
He found, for example, in preparing his sandy soils free 
from nitrogen, in which he proposed to grow lupines, 
that, in order to have these plants succeed, it was neces- 
sary to wet the sands with water leached from lands 



126 



The Soil. 



where these plants had habitually grown. The applica- 
tion of water from rich loams which had produced peas, 
beans, and vetches appeared to do them no good ; the 
inference being that these soils did not contain the 
bacteria which live upon their roots, while the natural 
lupine soils are rich in them. Experiments have been 
made in introducing the bacteria from the tubercles from 
pea roots directly into the roots of lupines, but without 




Fig. 18. — Showing the influence of free-nitrogen-fixing germs on the 
growth of peas. The large plants all grew in sand containing the 
nitrogen-fixing bacteria, while the small plants grew in soils iden- 
tically the same except that all bacteria were excluded from them. 
After Hellriegel. 

proving of any help to them. A full study of these 
problems may lead to an explanation of why it is some- 
times difficult at first to get clover to do well on certain 
soils, and also what is the cause of " clover-sick " lands. 

To show how great is the service of these free-nitrogen- 
fixing germs, there is given below the results of eight 
trials made by Hellriegel with lupines, in which all of 
the plants were treated alike except that four of them 



Free-Nitrogen-Fixing Grerms. 



127 



were, at the start, given loam water in order to add the 
necessary bacteria, while the other four pots received 
none. Taking the amount of nitrogen in the plants 
forced to grow unaided by the nitrogen-fixing germs as 
1, the amounts stand, — 




Fig. 19. — Showing the growth of rye, oats, peas, wheat, flax, and 
buckwheat in soils fertile in all elements of plant food except nitro- 
gen, and illustrating the power of the pea, through its root tuber- 
cles, to procure nitrogen from the air. After P. Wagner. 









Nitrogen. 








Nitrogen 


No. 1, 


without 


germs 


1 


No. 2, 


with 


germs 


76.07 


No. 3, 


it 


it 


1 


No. 4, 


c . 


1 1 


82.36 


No. 5, 


ti 


u 


1 


No. 6, 


u 


it 


91.15 


No. 7, 


u 


It 


1 


No. 8, 


tt 


1 1 


100.54 



If, however, we compare the weights of dry matter 
produced, these stand, — 







The Soil. 










Dry Matter. 






Dry Matter, 


.1, 


without germs 


l 


No. 


2, 


with germs 


48.66 


.. 3, 


u u 


l 


No. 


4, 


k it 


57.01 


'•5, 


u u 


l 


No. 


6, 


u u 


48.30 


-.7, 


u u 


1 


No. 


8, 


u it 


41.58 



These two comparisons bring into strong relief the 
great help the lupines received from the nitrogen-fixing 
germs which grow npon their roots ; for they show that, 
while there is a strong difference betw r een the amounts 
of dry matter produced under the two conditions, there 
is a much larger difference between the amounts of nitro- 
gen in the crops. 

The same facts are rendered still more emphatic in 
Fig. 18, which shows the results of growing peas in pots 
of soil in which all germs bad first been killed, and then 
introducing them again in one set but not in the other. 
In Fig. 19, too, will be seen how differently the plant 
thrives which can get the nitrogen it needs from the air 
through the aid of these germs than do those not able to 
profit by their help, while Fig. 20 shows the importance 
of nitric nitrogen to other plants. 

SYMBIOSIS. 

This living together of plants for their mutual benefit 
or symbiosis, as it has been technically called, is not a 
rare occurrence. Indeed the whole family of lichens, 
already referred to, are now regarded as examples of 
this phenomenon, the forms being in reality fungus, puff- 
ball or toadstool-like plants densely inhabited by green 
or chlorophyll-bearing algae. These two types of life 
live together to the advantage of both. And what is 
still more strange and interesting in this connection, is 



Symbiosis. 



129 



the observation that members of the animal kingdom, 
like the Radiolaria and Actinia?, owe their colors in part 
to the many minute, one-celled alga? living within their 
bodies, and there consuming the carbon dioxide given off 
by the animal and in their turn producing starch, under 
the action of sunlight, which serves as food for their 
host. 




Fig. 20. — Showing oats growing under conditions identical with those 
of Fig. 19, except that the several pots received Chile saltpetre, 
1, 2, and 3 grams respectively, thus enforcing the immense impor- 
tance to such plants of nitric nitrogen. After P. Wagner. 

Then, again, as a matter of immediate and practical 
importance to agriculture, it appears from the studies of 
Frank, and afterwards Schlosing, Jr., and Laurent in 
1891, followed by Kosswitsch in 1894, that there are 
in the soil certain nitrifying bacteria which, living in 
symbiotic relation with soil algae, are able to and do, 



130 The Soil 

under favorable conditions of light and moisture, fix 
considerable amounts of free nitrogen. Further than 
this, there is already at hand some evidence in favor of 
the view that even upon the soilless rock, which has 
become the abode of lichens, the process of fixing free 
nitrogen is there carried forward, if not through the 
double form of life which the lichen really is, then 
through the aid of a process similar to the one just 
mentioned. 

After what has been said regarding these sources of 
nitrogen in the soil, it may be asked, How then can there 
ever occur a deficiency of it ? The answer of course is 
that Nature, in her universal method of over and over 
again, has her counter processes of denitrification, of 
returning to the air from which it came the nitrogen, 
just as is the case with carbon dioxide ; and man, when he 
sets his will and his ignorance against natural methods, 
has often given these latter agencies the ascendency. 
This brings us to consider how the nitrogen, once fixed 
in the soil, is used by plants, and how it may be lost. 

NITRIFICATION AND DENITRIFICATION. 

It has not yet been satisfactorily determined in what 
form the nitrogen fixed by the bacteria living upon the 
roots of plants, is used by those species, but the general 
belief, regarding plants whose roots are not inhabited by 
nitrogen-fixing germs, is that they are almost wholly, if 
not entirely, dependent for their nitrogen supplies upon 
the nitric acid, and possibly also to some extent upon 
ammonia in the soil. We need, therefore, to learn how 
these substances are brought to the soil, and how they 
may be lost. 



Nitrification and Denitrification. 131 

We have already seen that some nitric acid and some 
ammonia come to the soil from the atmosphere directly, 
but in quantities too small to meet the demands for 
them. By far the larger part of the nitric acid found in 
soils is the final product of life processes there carried 
on when conditions are favorable for them to go forward. 

All are familiar with the odor of ammonia as it rises 
from the heap of fermenting manure. This ammonia is 
produced from the compounds of nitrogen in plant 
tissues and in the excretions of animals through the 
action of certain kinds of bacteria. The same process, 
too, takes place in the soil where organic matter decays, 
and through the same agencies ; but in the soil no sooner 
is the ammonia produced than it is seized upon by an- 
other organism, the nitrous ferment, and converted into 
nitrous acid. But the process does not end here ; for no 
sooner is the nitrous acid formed than it is seized upon 
by still another distinct kind of micro-organism and con- 
verted into nitric acid, when it becomes available to 
higher plants. 

It appears, therefore, from these facts, that we have in 
nature, so far as the nitrogen is concerned, a short-cir- 
cuit rotation, this element of plant food not starting from 
its free, uncombined state in the air and passing through 
the compounds of living tissues and then back to gaseous 
nitrogen again in each and every round. On the con- 
trary, there is a very large amount of nitrogen, in the 
form of nitric acid, being removed from the soil and 
transformed into the higher compounds of plant life, 
and then, after it has served its purposes in this form and 
the plants which have used it die, it passes back through 
ammonia and nitrous acid, reaching the nitric acid form 
again without having become nitrogen gas. Then too, 



132 The Soil 

when animals feed upon the higher plants, the circle in 
which nitrogen makes its round is widened, and it is 
rendered even still broader in those cases where flesh- 
eating animals place themselves in the circuit. 

There are, however, processes going on in nature 
whereby the nitrates may be, for the time, entirely lost 
to higher plants and animals, these compounds being 
sometimes borne away in the drainage waters to the sea, 
there to serve the purposes of marine life. Then, again, 
there live within our soils microscopic forms of life 
which, when a rich soil is kept over wet and not well 
ventilated, are able to live, not only upon the nitrates, 
converting them into free nitrogen gas, thus impoverish- 
ing the soil, but also to feed upon the organic compounds 
as well, here, too, restoring free nitrogen to the air. 

Dr. Angus Smith showed in 1867 that nitrates in 
sewage waters are decomposed with the liberation of free 
atmospheric nitrogen. Schlosing has also shown that 
a moist humic soil very quickly lost all traces of nitrates 
after being kept in an atmosphere devoid of free oxygen. 
Warington has shown that even sodium nitrate is de- 
composed in a water-logged soil, and a large part of the 
nitrogen set free as nitrogen gas. So great does the 
demand for oxygen appear to be in these water-soaked 
soils, that certain micro-organisms are even able, accord- 
ing to the observations of Mimtz, to withdraw it from 
chlorates, bromates, and iodates, leaving in their stead 
chlorides, bromides, and iodides. So too it has been 
shown that when suitable forms of organic matter are 
brought into the presence of nitrates, even though some 
oxygen be there, the life demands for it may be so urgent 
that the nitrates may be broken down and nitrogen gas 
set free. 



Nitrification and Denitrification. 133 

There is still another condition 11110161- which the proc- 
esses of denitrification take place. It is the rapid, large, 
and almost complete loss of nitrogen from human excre- 
ment, where dry earth is used in the dry-earth closets. 
Storer quotes from various authorities a considerable 
amount of evidence relating to this phase of the subject. 
One of the most striking cases cited, is that where Colonel 
Waring kept two tons of dry earth for a number of years, 
having it used over and over again in order to see how 
long it might be employed without losing its efficiency. 
It is stated that the closets were filled with this dry earth 
about six times each year, and that when the vaults Avere 
emptied the earth was thrown into a heap in a well-venti- 
lated cellar to dry. After this material had been used 
over not less than ten times, samples were sent to Pro- 
fessor Atwater for analysis. His examination showed 
that these ten-times-used soils contained no more than 11 
pounds of nitrogen in the 4000 pounds of soil, and yet it is 
estimated that not less than 230 pounds of nitrogen had 
been added and that not less than 3 pounds existed in the 
soil when it was taken for use. It thus appears that all 
but 8 pounds of the 230 pounds of nitrogen added to this 
dry soil had been, during the interval, converted into gas. 
Nor was this all. • So complete had been the destructive 
processes that nearly all the carbonaceous materials, 
including the paper used, had entirely disappeared. • 

Nature, then, so far as nitrogen compounds are con- 
cerned, just as with other matters, has her constructive 
and destructive processes pitted one against the other in 
such a manner that they tend all the while to balance. 
Go where you will, in almost any natural meadow or 
natural wood, and you will find growing there some plant 
of the leguminous species upon whose roots the free- 



134 The Soil. 

nitrogen-fixing bacteria have their home, and where they 
are performing that service so indispensable to the higher 
types of life. Living with these nitrogen gatherers, there 
are, of course, other species which feed upon the nitrogen 
compounds produced by the plants referred to, while still 
other forms return to the atmosphere the nitrogen in its 
free and uncombined form. But man, not understanding 
how the nitrogen supply of the soil must be maintained, 
has shut out completely for many years in succession the 
symbiotic life referred to, and has attempted to grow crop 
after crop of wheat and other plants able only to con- 
sume the nitrogen of the soil without adding appreciable 
amounts to it, and with the inevitable result that the 
available nitrogen supply has fallen below the level need- 
ful to large yields. 



CHAPTER IV. 

CAPILLARITY, SOLUTION, DIFFUSION, AND OSMOSIS. 

Before taking up the physical problems of the soil, it 
will be very helpful if we can first get a clear conception 
of the processes of capillarity, solution, diffusion, and 
osmosis. 

This is important, because they are the modes by which 
all the food of plants is conveyed to them, whether this 
food comes from the air or from the soil. 

Whenever a lamp is lighted, there is at once started 
a current of oil, rising from the bowl through the many 
interspaces between the threads of the loosely woven 
wick, and this flow continues so long as the oil is removed 
from the upper end by burning. So, too, when a wet soil 
is exposed to a drying wind, the removal of water from 
its surface results in setting up a flow from deep in the 
ground, upward toward and to the drying surface, to make 
good these losses. Then, again, when the root of a plant 
threads its way among the soil grains and withdraws from 
their surfaces a portion of the water with which they 
are charged, there is at once set up, to make good this 
loss, currents of water traveling from various directions 
in the soil toward the absorbing root. By what mechan- 
ism are these movements maintained, and what is the 
source of energy by which the work is performed ? 

When the water rises from a well through the action 
of the pump, we know that the energy generated in the 
muscles of some man's arm has been transferred, through 

135 



136 The Soil 

the pump handle and the piston, to the rising column of 
water ; or if not the energy of human muscles, then that 
from the moving wind, acting through the windmill, or 
some other equally evident source of power. Matter is 
never moved, work is never performed except at the 
expense of energy in one form or another ; so in the 
capillary movements of water through the soil, and in 
the rise of oil through the wick of a lamp, work is being 
done, and energy from some source must be expended. 

SURFACE TENSION AND CAPILLARITY. 

The first careful study of the rise of water in capillary 
tubes was made by Hauksbee nearly 200 years ago, but 
history shows that the phenomena were known to Leo- 
nardo da Vinci, the famous artist, who lived between 1452 
and 1519. But notwithstanding the large amount of very 
careful study which these phenomena have received even 
during recent years, we are yet in the dark as to just how 
the energy which forces the capillary fluids to move is 
transformed into current motion ; but all are agreed that 
it is in some way brought about through the surface ten- 
sion of liquids. 

During the blowing of soap bubbles, every one has 
observed that the bubble left hanging from the bowl of 
the pipe contracts, grows rapidly smaller, and forces a 
strong current of air out through the stem, showing that 
the thin film of water is acting like a stretched rubber 
ball. Now, if a large drop of water or a marble could be 
placed in the centre of the bubble, it is evident that the 
thin film would close down upon it, compressing it with 
so much force as it is able to exert, and in the case of the 
drop of water, the film would tend to keep it spherical in 



Surface Tension and Capillarity. 137 

form. Many different phenomena show that the free 
surfaces of all liquids act upon the mass within or 
beneath them very much as if they were elastic and 
contracting membranes, and the spherical form of the 
raindrop, of the melted lead as it falls from the shot 
tower, of the dewdrop on the cabbage leaf, and the 
spherule of water as it rolls along the dusty floor, or 
glides from side to side on the surface of a hot stove, 
each and all owe their shape to this surface tension. 
It is this surface tension which allows a polished needle, 
although seven times heavier than water, to float easily 
upon its surface, and it is advantage of this, too, which 
the water spider takes as it glides easily along the water 
surface of ponds and slow streams. 

This surface tension is a condition which results from 
the fact that all molecules in the surface of a liquid are 
being pulled more strongly into the liquid, by the mole- 
cules in the deeper portions of the liquid itself, than 
they are being drawn outward by the gaseous molecules 
of the air or vapor outside. In the interior of any liquid, 
after a very short distance below the surface is reached, 
each and every molecule is pulled on every side equally, 
so that a perfect balance of pulls exists. This makes it 
possible for the slightest disturbance to make these mole- 
cules move from place to place. But on the surface the 
molecules all behave as if they were being drawn into 
the liquid by a stretched rubber band or spring, and the 
strength of this pull is really something very great. It is 
because the pull toward the interior of a liquid is so strong 
that such large amounts of work are required to be done 
to convert a liquid into a gas, as in the case of changing 
water into steam. You set a basin of water on the stove, 
and work is being done through its bottom, Avhich tends 



138 The Soil. 

to drive, and does drive, the water molecules out through 
the surface film, but against a pressure which is enor- 
mous. Ostwald states that this pressure, for the liquid 
ether, amounts to something like 1284 atmospheres, or 
more than 9 tons to the square inch ; and yet the latent 
heat of water is nearly six times as great as that of 
ether. It is not strange, therefore, that to change a 
pound of water at 212° F. into steam at the same 
temperature, and under the pressure of 1 atmosphere, 
requires an amount of work which, when expressed in 
the terms of tons lifted against the force of gravity, finds 
its equivalent in no less than 37 tons lifted 10 feet high. 

These enormous pressures are not felt by bodies 
placed in the interior of water, because they are sur- 
rounded by a water surface which pushes away from the 
body with equal force. 

Now in the phenomena of capillarity a small part of 
these pressures are brought into play, giving rise to the 
movements of water in the soil, to the ascent of oil in 
the wick of a lamp, and to other similar phenomena. 

If a clean glass tube .055 inches in diameter is placed 
upright in pure water at a temperature near freezing, 
the water will be seen to rise on the inside to the height 
of 1 inch above the surface of the liquid in the vessel, 
and the smaller the diameter of the tube is the greater 
will be the height to which the water will rise in it, 
the height being inversely proportional to the size of the 
tube at the surface of the water within, as shown in the 
table below : — 



i a tube 1 


inch in diameter the water rises .054 inches. 


• 


U l< ^ 


a. u u u u it .545 " 


" " .01 


" " " " " " 5.45(5 " 




" » .00] 


it u 4<. it (< a. 54.5(3 " 





Surface Tension and Capillarity. 139 

To understand thoroughly just why water rises to a 
greater height in the narrow tubes than it does in the 
wider ones, will help us the more clearly to understand 
the capillary movements of water in the soil, and as the 
manner of action of the forces which produce the rise 
can be more simply stated for the tubes than for the 
soil itself, it will be best to explain the action as it takes 
place in the tubes first. 

Thrusting a clean glass tube beneath the surface of 
water and then withdrawing it, it comes forth wet, that 
is, with a layer of water adhering to it. This proves 
that the force acting between the molecules of water 
and those of the glass is stronger than the force acting 
between the molecules of the water ; for, were this not so, 
the glass must necessarily come from the water dry, just 
as it does when withdrawn from a dish of mercury. 

Not only is the attracting force of the glass molecules 
stronger than is that of the water molecules, but this 
force reaches out and is felt over some distance beyond 
the surface, a distance which Quincke estimates at not 
far from one five-hundred-thousandth of an inch. Now 
when the glass tube is thrust into the water, the row 
of glass molecules just above the water draw up toward 
them all around a row of water molecules ; but as these 
move up, other water molecules are made to follow, 
and the whole surface film is somewhat raised. When 
this lifting process is once started, it goes on until so 
much water has been lifted above the level of the water 
in the vessel as will balance, by its weight, the total pull 
of the molecules in the wall of the glass tube at the 
margin of the surface film. 

Now, as the circumferences of cylindrical tubes in- 
crease in length in the same ratio as their diameters do, 



140 The Soil. 

it is plain that if we take the distance around a tube 
whose diameter is .001 of an inch as 1, then in the case of 
tubes whose diameters are .01, .1, and 1 inch respectively, 
their circumferences will be 10, 100, and 1000 times as long. 
Their walls will also contain 10, 100, and 1000 times as 
many molecules, and as each and every molecule is able 
to do a like amount of work, it follows that the total work 
done by the walls of these several tubes in lifting water 
will stand in the relation of 1 to 10, to 100, to 1000. 

But the areas of the cross-sections of these tubes, and 
their volumes also, grow larger in the ratio of the 
squares of their diameters, so that the surfaces of the 
columns of water in the several tubes will be in the ratio 
of 1, 100, 10,000, and 1,000,000, where their diameters 
are 1, 10, 100, and 1000 respectively. 

We have seen before that the height to which the 
surface of the water is raised is the greater the smaller 
the diameter of the tube, so that if we call the height 
to which the largest tube raises its water 1, then the 
heights in the other cases will be 10, 100, and 1000. 
But only the very surface layer of water is raised 
through these heights, while the bottom layer has not 
been lifted, and, this being true, the average height 
through which the water has been raised in each case 
will be .5, 5, 50, and 500. 

Now to get a relative measure of the amount of work 
done in each case, we must multiply the mean height of 
the respective columns by their areas, and, doing so, we 
have, — eelative 

Mean Height. 

For the 1 inch tube . 5 

" " .1 " " 5.0 

" " .01 " " 50.0 

» " .001 " " 500.0 







Total 


Eelative 


Area. 


w 


okk Done. 


Work Done. 


)00000 




500000 


1000 


10000 




50000 


100 


100 




5000 


10 


1 




500 


1 



Surface Tension and Capillarity. 141 

It is here seen that while the amount of water lifted, 
or the work clone, by the walls of the largest tube is 
much more than that done by the smallest tube, it is 
only so much more as the number of molecules constitut- 
ing its circumference is greater. It is also seen that 
before the molecules in the walls of the smaller tubes 
have accomplished relatively the same amount of work 
as those in the walls of the larger tubes, they must 
necessarily have lifted their columns of water higher, 
and because the weight of the water in the column 
increases as the square of the diameters of the tubes, 
but only directly as the heights. 

In order to apply these principles to the capillary 
movement of water in the soil, we need to call to mind 
the cavities or openings which are left between the soil 
grains, which are similar to, but much more irregular, 
than those left between shot when they are filled into a 
dish. While these cavities do not form straight capil- 
lary tubes leading from deep in the ground to the sur- 
face, they do in fact form broken or zigzag passageways 
which in effect act in the manner of the capillary tubes, 
but with- greater resistance to flow, on account of the 
water being forced, during the course of its rise, to 
change its direction so many times before reaching the 
surface of the ground or the root of a plant. 

If we ask ourselves how much work this surface 
tension, or capillary power, is able to do, the answer 
must be sought in the amount of water which can be 
raised by it through a known height in a given time. 
The writer has found that a very fine sand did lift water 
through four feet at the rate of .91 pounds per square 
foot in twenty-four hours, while a clay loam lifted it at 
the rate of .9 pounds per square foot through the same 



142 The Soil. 

distance in the same time. Now, this amount of work, 
when measured in horse power of 550 pounds lifted one 
foot high per second, is very small ; so small indeed is 
it, that one horse power may do the effective work of 
the surface tension for 302 acres when moving water at 
the observed rate mentioned above. 

It would be a very grave mistake, however, to conclude 
that because this form of energy is so small in amount, we 
may pay no heed to it. On the contrary, it is because 
the amount of work it can do is so small that it becomes 
of the utmost importance to so manage the soil as to 
enable it to act under the most favorable conditions. 
And when it is stated that this surface tension is the 
only available power for moving the water of the soil to 
the roots of plants, then there can be no question regard- 
ing the importance of all those processes which tend to 
favor capillary movement and the conservation of soil 
moisture. 

THE NATURE OF SOLUTION. 

Let us now consider the process of solution, the means 
by which the soil gives to the capillary water the ash 
ingredients and the nitrogen compounds of plant food. 
The real nature of this process will be most easily under- 
stood if we first consider what takes place when Ave 
detect the odor of some fragrant flower or the perfume 
from some unstoppled bottle placed at a distance from us. 
In these cases there are traveling away from the blossom, 
or from the open bottle, molecules of that substance 
whose odor we detect; these perfumes are going into 
solution in the air, and we detect them as they are 
brought into contact with the organs of smell. We 



The Nature of Solution. 143 

know there is a movement of the perfume in these cases, 
because they reach us at a distance ; we know, too, that 
this movement is taking place in all directions, and at the 
same time, because, on whatever side we stand, the odor 
comes to us. We know, too, that these molecules tend to 
spread wider and wider, until the whole air has been 
permeated with them. The evaporation of water is 
simply another case of solution in the air, where the 
water molecules, through the absorption of heat, have 
been so violently disturbed as to be thrown beyond the 
sphere of molecular attraction in the liquid, when they 
become a gas and travel indiscriminately in all directions 
through the air. 

When a lump of salt or of sugar is dropped to the 
bottom of a vessel of water, our experience has demon- 
strated time and again that, after a longer or a shorter 
interval, and in spite of the fact that these substances 
are heavier than water, they will be found uniformly 
distributed throughout the whole. Here, too, the mole- 
cules of sugar or of salt wander about from place to 
place in the water, until there is no portion of it they 
have not reached. At the outset, the action of surface 
tension results in overcoming the cohesive or binding 
power which makes the sugar a solid. Its molecules are 
being dislodged, and, once free to move, they are never 
again relatively at rest until some cause is brought into 
operation to convert them once more into a solid. 

So, too, when water is brought into contact with the sur- 
face of soil grains, or particles of various kinds of fertili- 
zers which may chance to be present among them, there 
is here set up a disengagement of the surface molecules, 
and these, finding themselves free in the capillary water, 
travel from place to place in it, or they are borne along 



144 The Soil. 

with, the current movements as they rise to meet the 
losses due to evaporation, and pass laterally to make good 
the amounts withdrawn by the roots of plants. 

Nearly all substances dissolve more rapidly at high tem- 
peratures than at low, so that a warm soil prepares food 
faster than a cold one can, and this brings us to consider 
the work which altered sunshine does in the prepara- 
tion and movement of plant food in the soil. In speak- 
ing of the surface tension of liquids, we have referred to 
the strong power which is exerted among the molecules, 
tending to draw them together, and which is only over- 
come through the expenditure of an enormous amount of 
heat energy when evaporation takes place. Now, as a 
basis for understanding the solution of plant food in soil 
water, let us get clearly in mind that, fundamentally, the 
solution of a solid in water is not very different from the 
evaporation of water in air, and let us keep in mind, too, 
that, strong as the attractive force is between molecule 
and molecule of water, the dynamic effects of heat are 
great enough, even when water is frozen into solid ice, to 
throw its molecules entirely beyond the bounds of cohe- 
sive attraction, thus causing frozen garments to dry 
rapidly even when hung in an atmosphere far below freez- 
ing. Solid camphor evaporates, too, as we know from its 
odor, under the dynamic action of heat. 

We have seen that it is only the surface molecules 
of water which find great difficulty in moving from 
place to place. Within the liquid mass the forces are 
very great, but so nearly balanced on all sides that only 
a little heat energy is required to cause a movement. 
So, too, in the case of the soil grains, the surface mole- 
cules are under a strong tension, which makes it ex- 
tremely difficult for altered sunshine to throw any 






The Nature of Solution. 145 

of them out, or, in other words, to cause them to 
evaporate. 

But when a soil grain becomes invested by a film of 
water, this water, through its strong outward action, so 
much weakens the surface tension of the soil grain that 
the absorbed heat, the altered sunshine, is now able 
to throw some of its molecules through the surface film 
and into the water outside, thus dissolving it, and 
this process of solution will go on until the water which 
surrounds the soil grain has become saturated with the 
dissolved substance. 

Through the studies of van't Hoff, W. Nernst and 
others, it appears that water saturated with a dissolved 
solid is not widely different from air saturated with 
water ; and it is now generally agreed that a saturated 
air is simply one so full of flying molecules of water 
that just as many of them fall back again into the water 
each second of time as are driven out of it through the 
action of heat. In this view evaporation has not stopped, 
but rather the rate of condensation has come to equal 
the rate of evaporation. If, however, the temperature 
should fall, then the stream of outflowing molecules 
would become smaller, because the engine is slowing 
down, while the incoming molecules, reaching the water, 
remain there, thus rendering the air drier. On the 
other hand if, when the air has become saturated, the 
temperature of both air and water should rise, — that is, 
if altered sunshine should enter the water at a more 
rapid rate, — then more Avater molecules would be forced 
out each second than, for the time being, are returned 
to it, and hence evaporation would commence again and 
the air would come to contain a higher per cent of 
moisture. It would be a stronger solution. 



1 16 Soil 

[f W6 rarrv this method ol work to the solution of 

plant food in the soil, we shall understand that, as the 
ground warms up in the spring, as the altered sunshine 
becomes more concentrated in the soil grains, as the 
molecular swing becomes stronger and stronger, the rate 
at which the molecules of plant food are driven on1 into 
the Rim of water mounts higher and higher until finally 
the soil water, like the atmosphere, has become saturated. 
In this condition the play back upon the soil grains is 
equaled by the outward discharge, and a balance is 
reached, but not a condition o( rest ; for solution and 
precipitation are going on even-handed. If the tem- 
perature of the soil should go up, then t ho amount o( 
plant food in solution would increase; while if it should 
fall, then some ^\ the dissolved materials would again 
take on the solid form. 

On the Other hand, if the root hairs of plants, or the 
cell w* the mw ^( the soil, come in 

a the water in which this pr< ess of solution 
is I ed on. and they utilise a portion of these 

Is, then the) will cause the solution 
to go forward at a more rapid rate, ilution will 

bo more vapid because every outgoing molecule which is 

n returning, \ g heavj 

w, bj so much 9 the resistance which the 

out molecules are me, 

w v must not ' lit of the fact, in this connection, 

thai ment « hu b bears the dis 

d materials of the ground and to 

the aust in some way represent altered 

sunshine, Somehow the molecular - of the - 

is transformed into current tlow ; for a stream 

,-'.\ through I 



Osmosis and Diffusion in l*l<itit Feeding, I 1 7 

whole summer through, against gravity, against the fric- 
tion of the very great soil surface, and against the resist- 
anoe necessitated by the many turns the currents are 
forced i<> take, without the expenditure of much more 
energy bhan is represented by bhe amount of water lifted! 

OSMOSIS AND DIFFUSION TH PLANT WEEDING. 

We have seen how altered sunshine, working through 
the soil moisture, brings into liquid form fche food <>r 
plants ; we have seen, too, how this prepared food is borne 
along in the capillary currents to the places where it is to 
be used. Let us next consider how the food laden water, 
after reaching the coot hairs, is made bo enter them and 
rise through the sinus into i he Leaves and sunshine abovoi 

The process by which this work has been accomplished 
has been technically named osmosis, and we have been 
made perfectly familiar with some of its results in many 
ways. When <li,y beans, prunes, or raisins are put in 
water bo soak, it is not long before they have increased 
in size through the absorption of water. Osmosis has 
taken place in each of these cases, and bhey illustrate, 
so far as the real mode of action is concerned, the How 
of sap in plants. When juicy fruits are covered with 
sugar or are placed in a strong syrup, they shrivel and 
become much Bmaller; here, too, osmosis has occurred, 
but the strongest movements have taken place in the 
opposite direction. In both <>r these classes of oases 
movements have taken place, very similar bo evaporation 
and to solution, and bhe dynamic power of heat or the en 
ergy of molecular motion has been bhe actuating energy. 

In trying bo understand bhis process as it comes into 
play in the feeding of plants, we need first to oonsidei 



148 The Soil 

some physical experiments which have served to demon- 
strate the intensity of pressures which, under favorable 
conditions, are developed during the action of osmosis. 
The swelling of the dry bean to two or three times its 
original volume certainly represents no small amount 
of pressure ; for it is evident enough that, could we con- 
nect a column of water with the bean and undertake 
to distend it by direct hydrostatic pressure, a very high 
column of water would be required to do the work. 

Abbe Nollet, who lived between 1700 and 1770, appears 
to have been the first to record that, if a glass vessel 
be filled with wine and covered with a bladder and 
then immersed in water, the contents of the vessel 
would increase and sometimes to such an extent as to 
burst the membrane. The same fact was rediscovered 
a second, third, and even a fourth time before it came 
to be the common property of science and was thor- 
oughly investigated. 

It was reserved, however, for W. Pfeffer, in 1877, to 
conduct experiments in osmosis under such conditions 
that a full measure of its power could be obtained. He 
used a porous clay cell, lined with a membrane, produced 
by precipitating on its inner wall a coating of copper fer- 
rocyanide. Attaching a pressure gauge to this, he found 
that when this cell was filled with a solution containing 
1.5 per cent of potassium nitrate and then set in a vessel 
of pure water, the water continued to flow into it until a 
pressure of 3 atmospheres had been reached, and this is 
equivalent to a column of water at sea level, more than 
100 feet high ; while de Vries showed that a solution of 
potassium citrate developed a pressure of more than 5 
atmospheres, equal to a column of water rising to a height 
of 170 feet, or a pressure exceeding 70 pounds to the 






Osmosis and Diffusion in Plant Feeding. 149 

square inch. It is not strange, therefore, that dry beans 
swell when placed in water, nor that dry wood, when be- 
coming A\ r et, exerts such high pressure. 

When two dissolved or liquid substances are separated 
by a membrane through which one of these liquids can 
pass more readily than the other, then that liquid whose 
molecules are small enough to enable them to make their 
way through the separating membrane most rapidly, does 
so. This causes an accumulation, within the bean, for 
example, thus increasing its volume and at the same 
time the pressure. Under these conditions the mole- 
cules of water wandering about or diffusing, impelled 
by their heat energy, continue to pass through the por- 
ous membrane, continue to pass into the bean, until the 
same number, in their vagrant wandering, tend to emerge 
from the porous membrane, from the bean, each second 
of time, as tend to enter it. When this state has been 
reached, the in-and-out play goes on even-handed, a bal- 
ance has been reached, and apparent change has stopped ; 
a condition similar to air saturated with water has been 
attained. 

We may consider first the movement of water in and 
through the plant. If in any plant cell water is being 
consumed as food, if it is being changed into some other 
substance, or if it is evaporating and leaving the cell in 
this way, the removal of these molecules from the solu- 
tion leaves space unoccupied, diminishes the osmotic 
pressure at that place, and this diminution of pressure 
causes a flow of molecules from contiguous cells to 
make good this loss. Suppose that in a certain portion 
of a plant water is being used in the manufacture of sugar 
or starch. Then so long as this demand continues, there 
will be a lowering of the osmotic water pressure, and so 



150 The Soil 

long will water move toward that place. It is as if there 
were a long line of vessels full of water, all of them con- 
nected by means of pipes, and at one end of the line 
water is being dipped out, so that the water level or pres- 
sure in that is being lowered. When this is done, water 
Avill flow from the nearest vessel to take the place of 
that which has been removed, but no sooner is the water 
pressure or level in the second vessel lowered than a 
flow sets in from the third, and this to be followed by- 
water from the fourth, fifth, and so on to the end of the 
line. Then, if water is added to the far end of the line 
as rapidly as it is being removed at the other, a continu- 
ous flow will be maintained. On the other hand, if the 
dipping ceases, then the water surface becomes level 
throughout the whole system, the water pressure be- 
comes uniform, and flow ceases. 

Now in the case of the plant supposed, the diminution 
of the osmotic water pressure at the place of growth is 
propagated backward toward the end root hairs in the 
ground, and so soon as some of the root cells which are 
in contact with the soil water have their pressure re- 
duced by the flow toward the place where the water 
is being used, then the balance of pressure between 
the water in the root hairs and that which is in contact 
outside is destroyed, and more molecules enter than escape, 
impelled by the dynamic energy of molecular swing. So, 
too, if the reduction of osmotic pressure in the leaves is 
due to evaporation rather than the fixation of water, 
the same result follows. 

Then regarding the movement of nitrates from the 
soil into and through the plant ; so • long as there is 
no consumption of this substance in the tissues, just so 
many molecules of the nitrate, impelled by altered sun- 



Osmosis and Diffusion in Plant Feeding. 151 

shine, leave the soil water and wander through the fluids of 
the plant as are required to produce a balance of osmotic 
pressure throughout it, or, what is the same thing, an even 
distribution of nitrate in the sap. Under these condi- 
tions accumulation ceases. If, however, growth is going 
on which results in the removal and fixation of the nitrate, 
then, where this is taking place, the back play of the 
molecules is reduced, the balance is destroyed, and more 
nitrate advances to make good the loss ; a flow sets in 
from the soil toward the place of consumption. 

It follows from what has been said regarding osmotic 
pressure and its action, that there is a tendency for each 
ingredient of plant food to travel in a large measure in- 
dependently of every other material, the movements not 
being in the nature of currents. So that if the escape 
of water from the plant were to be stopped altogether, 
the osmotic pressure might be fully able to convey 
nitrogen and the ash ingredients to the plant dissolved 
in the water which, under these conditions, would act 
simply as a medium through which the diffusion is 
carried on. 

It will also be understood from these statements that 
the transfer of the assimilated products to the places 
where they are stored, whether in the seeds, thickened 
leaves, or fleshy roots and tubers, must also be effected 
by this process of diffusion through osmotic pressure. 
As the soluble forms, out of which the insoluble 
starches, gums, and fats are constructed, are withdrawn 
from solution, at their respective places, there must 
necessarily result a diminished pressure in the ear of 
corn, in the head of wheat, in the expanding apple 
and in the tubers of the potato, the bulb of the onion or 
the root of the carrot, toward which the products com- 



152 The Soil. 

pounded in the green parts of the plants must be im- 
pelled by the energy of altered sunshine. 

In justice to the reader and to the truth, it should be 
said in closing this subject that not all physiologists are 
fully agreed that osmotic pressure is the only power 
which actuates the movement of sap in plants, but the 
most reliable data we now have go to show that it is the 
prime, if not the sole, mover, and to this physiologists 
are agreed. 

The so-called selective power of plants, whereby they 
obtain those substances dissolved in the soil water which 
contribute to growth, and those substances which are 
brought into solution by the corroding power of juices 
exuded from their roots, finds its explanation in osmotic 
pressure. Regarding this point, it should be understood 
that any substance held in solution in the soil water may 
make its way through the tissues of plants, and usually 
does so until the sap contains the same number of mole- 
cules per unit volume as the soil water contains. Under 
these conditions, if that substance is not being used by 
the plant, no further accumulation of it can take place ; 
for the outflow from the root into the soil keeps exact 
pace with the inflow from the soil toward the tissues. 
The loss of water by evaporation through the surface of 
the plant or the consumption of it as food, which tends 
to make the strength of the solution of those substances 
not used as food stronger, cannot result in a permanent 
increase of them in the plant, because, unless these sub- 
stances are actually taken out of solution, they travel 
back toward the root again and escape into the soil water 
so long as the solution inside is stronger than is that out- 
side. 

If the molecules of any substance in solution are too 



Osmosis and Diffusion in Plant Feeding. 153 

large to easily make their way through the walls of root 
hairs, as seems to be the case with some of the colloidal 
salts, then there is a positive exclusion of these sub- 
stances from the plant, or they only enter in diminished 
quantities, just as the colloidal substances in the plant 
cells do not readily escape into the soil water under the 
impulse of this osmotic pressure. 

So, too, when a soil contains any substance which is 
poisonous to the plant or which by its presence in the 
sap would be harmful, the roots have no power to exclude 
it. The process of osmosis tends to carry it to all parts 
of the plant, just as when a soluble poison is taken into 
the stomach of an animal it is absorbed and goes quickly 
through the system. 

The plant then simply takes out of the solution brought 
to it those substances which it needs. It is not overloaded 
with other substances, because it leaves those in solution, 
and this is a sufficient check to a further accumulation of 
them. 



CHAPTER V. 

SOIL WATER. 

From what has been said in the preceding chapter, it 
is evident that water plays an extremely important part 
in the fertility of soils and in the feeding and life of the 
plant. Surrounding the soil grains as a surface film, it 
acts directly upon even the most difficultly soluble of the 
soil ingredients, taking them into solution in larger or 
smaller quantities. Holding carbonic, humic, and other 
acids in solution and bringing them into close contact with 
the surfaces of the soil grains under a diminished surface 
tension, these substances are enabled to bring into soluble 
form the ash ingredients of plant food as they could not 
without the aid of water. Wood kept permanently so dry 
that it contains only a small amount of hygroscopic mois- 
ture never decays, and such perishable articles as fruits 
and even flesh may be preserved for indefinite periods of 
time if only they are kept permanently dry; and so in the 
return of dead organic matter in the soil to the ash in- 
gredients, nitrates and carbon dioxide, the forms in which 
they can be used over again by higher plants, the pres- 
ence of a certain amount of soil moisture is indispensable. 

After the plant food has been prepared in the soil or 
in the air, it is useless until endowed with the possibilities 
of movement toward and through the living tissues. But 
water, through the action of capillarity and osmotic pres- 
sure, is the medium of transport by which the ash ingredi- 
ents and the nitrogen of the soil are moved to the roots 

154 



Amount of Water Used by Crops. 155 

of plants, by which they are drifted into the sunshine of 
the laboratories in the green leaves and bark, and from 
which they are again taken to their final places in the 
structure of the plant. Nor is this all, for water is itself 
a food substance used in large quantities by all plants of 
whatever sort. By its evaporation from the foliage of 
plants, it not only holds the temperature down within the 
normal range of the vital processes there going on, but, 
because of this lowering of the temperature, it also hastens 
the osmotic flow of sap toward the leaves. 

AMOUNT OF WATER USED BY CROPS. 

The amount of water demanded by crops under our 
methods of culture is very large. So large, indeed, that 
in Wisconsin the following amounts in tons of water per 
ton of dry matter and in inches of water per ton have 
been lost by transpiration through the plant and evapora- 
tion from the soil : — 

Dent corn used 309.8 T. equal to 2.64 in. of water per 1 T. of dry matter. 



Flint " " 


233.9 " 


a 


2.14 " 


<< 


it 


it 


1 " 


a a it 


Red clover " 


4~)2.8 " 


u 


4.03 " 


ti 


it 


a 


1 " 


a it it 


Barley used 


392.9 " 


<< 


3.43 " 


u 


it 


a 


1 " 


it a it 


Oats 


522.4 " 


a 


4.76 " 


a 


a 


it 


1" 


it a a 


Field peas used 477.4 " 


(< 


4.21 ". 


tt 


a 


a 


1 " 


tt n a 


Potatoes used 


422.7 " 


it 


3.73 " 


it 


a 


a 


1 " 


a a a 



Hellriegel found, through experiments conducted in 
Prussia, that the amounts of water withdrawn from the 
soil and given to the air, almost wholly through the 
plant, were as follows : — 

Barley used 310 pounds of water for each pound of 
dry matter produced, summer rye 353 pounds, oats 376 
pounds, summer wheat 338 pounds, horse beans 282 
pounds, peas 273 pounds, red clover 310 pounds, and 



156 The Soil. 

buckwheat 363 pounds of water for one pound of dry 
matter. This is at the mean rate of 325 tons of water 
for each ton of dry matter produced. 

These large amounts of water used by vegetation in 
the maintenance of its functions are necessitated partly 
by the rapid evaporation which results from the extreme 
exposure of the foliage under conditions best suited to 
facilitate a rapid loss of water in this way ; but evidently 
also, in no small degree, by the physiological processes 
of the plant itself, which demand a large movement of 
water through the growing tissues. 

The fact, however, that the growth of vegetation is 
often extremely rapid during the times when the rate of 
evaporation must be relatively slow, makes it appear more 
than probable that the large losses of water by evapora- 
tion from cultivated fields, through the transpiration of 
growing crops, is not really demanded, so far as the needs 
of growth are concerned ; and if this is true, it follows 
that wherever we can adopt means which tend to avoid 
needless loss of water through the foliage of plants, we 
are practicing economy regarding soil moisture just as 
we are in our methods of mulching, by cultivation or 
otherwise, which aim to reduce the evaporation from the 
surface of the soil. 

There are very few countries, indeed, where the distri- 
bution of rainfall in time and amount is such as to permit 
fertile soils to produce the largest crops they are able to 
bear ; and this being true, those soils which are able to 
store the largest quantities of rain in a condition which 
shall permit vegetation to use it to the best advantage 
are likely to be the most productive. On this account 
the water capacity of soils is an important factor in the 
determination of land values. 



Capacity of Soils to Hold Water. 157 

CAPACITY OF SOILS TO HOLD WATER. 

Since each independent soil grain of a moist soil is 
more or less completely surrounded by a film of water, it 
is evident that, other conditions being the same, that soil 
whose grains present the largest aggregate surface area 
may retain the most water per cubic foot. Now a cubic 
foot of marbles one inch in diameter possesses an aggre- 
gate surface of 37.7 square feet, while if the marbles 
were reduced in diameter to one one-thousandth of an 
inch, then the total area per cubic foot is increased to 
37,700 square feet. From these differences it is evident 
that the amounts of water coarse and fine grained soils 
retain will be very different. 

Under field conditions the amount of water a soil can 
hold varies, not simply with the size of the soil grains, 
but also with the distance of standing water in the 
ground below the surface and the length of time which 
has elapsed since it has rained. 

To illustrate the influence of the size of the soil grains 
on the amount of water a soil may retain, let me cite 
some observations upon columns of sand 10 feet long, 
from which water had been allowed to percolate during 
111 days under conditions where no evaporation could 
take place from their surfaces. The column whose mean 
grains had diameters of y-jj-fl-o of an inch contained, in 
the upper 30 inches, 2.16 per cent, in the second 30 
inches, 2.41 per cent, in the third 30 inches, 2.73 per 
cent, and in the fourth, 7.77 per cent ; but a sand whose 
average grains were T7 4 oVo of an inch in diameter retained 
3.06 per cent for the upper, 3.71 per cent for the second, 
5.46 per cent for the third, and 18.05 per cent for the 
lower 30 inches. The first column had retained only 



158 The Soil. 

3.77 per cent of its dry weight of water, while the second, 
or finer, one had retained 7.57 per cent of its dry weight, 
or about twice the amount. Two other sands, with grains 
about 1 7 3 -q- and yo 6 oVo of an inch in diameter, placed 
under the same conditions, had retained 4.92 and 5.76 
per cent respectively ; that is to say, columns of sand 10 
feet long composed of grains 



ToMo °* an 


inch in diameter retained 3.77 


per cent of water, 


73 IC 

Toooo 


it k 


ct 


4.92 


u 


(< 


61 u 
10000 


U (< 


u 


5.76 


(( 


u 


45 U 
10000 


(t (< 


u 


7.57 


l( 


It 



after a period of percolation of 111 days. 

It will be understood that the smaller the size of the 
soil grains, the smaller will be the size of the pores 
through which the water is obliged to flow in percolating 
downward under the influence of gravity, and hence the 
slower will be the rate at which it will move. 

The table given below will show the influence of the 
size of the soil grains on the rate at which the water 
may be lost by percolation downward. The results here 
given were obtained from columns of sand 8 feet long, 
and composed of grains having the same diameters as 
those just referred to. 

At the end of 9 days these several soils had lost 
water, in the order from the coarsest to the finest, 15.29, 
14.35, 12.86, 10.02, and 8.42 per cent respectively of 
the dry weight of the sand. 

A strange thing about these soils is that they con- 
tinued percolating slowly for more than 259 days, and dur- 
ing the last 250 days they lost respectively, beginning 
with the coarsest, at the rate of 9.15, 7.77, 6.56, 7.69, 
and 7. 56 pounds of water for each square foot of surface, 



Capacity of Soils to Hold Water. 



159 



RATE OF PERCOLATION FROM EIGHT FEET OF SAND OF 
DIFFERENT DEGREES OF FINENESS. 





Time of Percolation. 




1 Hour. 


2 Hours. 24 Hours. 


48 Hours. 


tU fa of an inch • • • 

To¥o Of an inGh • • • 
ToVo Of an illCn • • ' 
ToVo Of an inGh ' • ' 
ToVoo Of an inch ' ' • 


Per cent. 

9.10 
7.95 
6.22 
1.76 

1.28 


Per cent. 
10.45 
9.47 
9.21 
2.83 
1.91 


Per rent. 

13.05 

12.31 

11.71 

7.64 

5.83 


Per cent. 

13.52 

12.72 

11.53 

8.44 

6.79 



amounts ranging from 1.2 to 1.8 inches of rain; nor had 
percolation at this time ceased. 

It must be understood that with true soils of much 
finer texture, the rate of percolation from them would in 
all probability be much slower and the water-holding 
power much larger, but no measurements have been made 
for any of these under the conditions stated above. 

To show what actual field soils may hold when their 
surfaces are only 11 inches above standing water, this 
water having been lifted into them by capillarity, the fol- 
lowing results may be cited : — 





Per cent of 
Water. 


Lbs. of 
Water. 


Inches of 
Water. 


Surface foot of clay loam contained 
Second " reddish clay " 
Third " " " " 
Fourth " clay and sand " 
Fifth " fine sand " 


32.2 
23.8 
24.5 
22.6 
17.5 


23.9 

22.2 
22.7 
22.1 
19.6 


4.59 
4.26 
4.37 
4.25 

3.77 


Total 


. . . 


110.5 


21.24 



Mat 16. 


July 13. 


Aug. 30. 


per cent. 


per cent. 


per cent. 


25.77 


24.27 
23.62 


24.71 
24.30 


22.87 


23.52 
23.32 


24.03 
22.29 



160 The Soil. 

Then, again, to show the water-holding power of natural 
soils under field conditions, the table below gives the 
water content of a piece of fallow ground at three differ- 
ent times during the season, the soil being a medium clay- 
loam with clay subsoil in the second and third feet and 
followed with sand in the fourth foot. The field was tile 
drained, the drains being 4 feet below the surface of 
the ground. 

Depth. 

First foot 1 
Second foot] 
Third foot 1 
Fourth foot { 

Average 24.32 23.68 23.83 

It is evident from the cases cited that the water-hold- 
ing power of soils under field conditions is really large, 
and that, where there is no crop upon the ground to con- 
sume the water, and the water table is not more than 
5 feet below the surface, the ordinary summer rainfall, 
assisted by capillarity, may nearly conpensate for the 
loss of water by percolation and by surface evaporation ; 
but this is far from being true when a crop is occupying 
the land, unless the rainfall is more than usually heavy 
and frequent. 

It may be said in general, regarding the capacity of 
soils to hold water, that the finer the soil grains the more 
the soil will hold, and the greater the number of spaces 
which are larger than capillary size the less it will hold. 
The capacity of a soil for water decreases to some extent 
also as its temperature rises, but under field conditions 
the effects of temperature are not large. It is certainly 
true for sandy soils that their capacity for water de- 



Capacity of Soils to Hold Water. 161 

creases in a marked manner the higher their surfaces 
are above standing water, and it is probably true that all 
soils, unless we must except the finest clays, fall under 
the same law. 

If it were true that all of the water which a soil may 
retain were available to crops, and it were not neces- 
sary to allow some of the water of completely saturated 
soils to percolate away before agricultural plants will 
thrive in them, then in most humid regions it would be 
possible to obtain much larger crops than can now be 
raised without irrigation. The facts are that not only 
must a considerable amount of the soil moisture be left 
unused by the crop, if large yields are expected, but from 
30 to 40 per cent of their saturation amounts must have 
drained away before the soil can contain air enough to 
maintain the breathing of ordinary roots and germinat- 
ing seeds. Hellriegel places the amount of water which 
should drain away from the soil before it becomes habi- 
table by cultivated plants as high as 40 to 50 per cent of 
their full capacity, and in order that maximum results 
may be reached, the water content should not fall very 
far below these amounts. 

The soils having a small water capacity will yield their 
water to plants more readily and completely than the 
heavier types. The writer has observed that, in a sandy 
soil whose maximum water capacity was about 18 per 
cent, corn was able to draw the water in it down to 4.17 
per cent, while in a clay soil, having a water capacity of 
about 26 per cent and lying nearer the surface and far- 
ther from standing water in the ground, the same plant 
had only succeeded in using the water down to 11.79 
per cent. 

Now if we compare the absolute amounts of water 



162 The Soil. 

given over to the corn by these soils, we shall find that 
the sandy soil contributed 13.83 pounds of its amount 
per cubic foot, while the clay had only yielded 12.5 
pounds. It thus becomes evident that while the percen- 
tage capacity of the sandy soil is much below that of the 
clay, its greater weight per cubic foot and the greater 
freedom with which it yields water to plants makes its 
storage capacity of available water more nearly equal to 
that of the loamy clay than would at first be supposed. 
It is on this account, in part, that a sandy soil, kept well 
fertilized, has many advantages over the colder, less per- 
fectly aerated, and more obstinate clayey ones, which 
crack badly in excessively dry weather and become over- 
saturated in wet seasons. 

It follows from what has been said regarding the 
capacity of long columns of soil for water, that the dis- 
tance of standing water below the surface, or below the 
level to which the roots of cultivated crops may reach, 
must materially influence their agricultural value. In 
general the nearer the surface of the ground water or 
water table is maintained to the lower surface of the 
root zone, the more productive the lands will be ; for then 
capillarity is able to hold the water content of the soil 
more nearly up to the standard required for maximum 
yields. This is the chief reason why lands which 
require underdraining are so valuable when they have 
been thus improved. 

THE GROUND WATER AND WELLS. 

In all humid climates where the soil, or unsolidified 
sand and gravel, has a depth of 50 to 200 feet, there is 
a certain distance below the surface at which all of the 



The Ground Water and Wells. 163 

interspaces between the incoherent grains are completely 
filled with water, and the upper surface of this water- 
filled soil is called the water table. Above this water 
table the soil contains only capillary water. When 
wells are sunk into the water-filled soil, the surface of 
the water in these wells represents the level of the 
water table, at that place. We should think of all per- 
manent lakes and ponds, too, as extensions of the water 
table, where the surfaces of low lands are beneath it. 
It must not be understood, however, that the height 
of the water table under the land is at the level of the 
water in the lakes. On the contrary, the water table 
almost invariably rises as the distance from the mar- 
gins of lakes and other permanent bodies of water 
increases. Indeed, the surface of the water table fol- 
lows in a rough way the general contour of the land, the 
water-filled soil beneath the surface standing highest 
where the ground is highest, and lowest where the land 
is low. The water table has -its hills and valleys, which 
coincide with those of the country it underlies, only they 
are not as steep, the water being nearer the surface 
under the low ground than it is under the high. An 
inspection of Figs. 21 and 22 will show how the ground 
water is related to the surface in one locality. In one 
of these figures the contour lines show the surface of the 
land, while in the other they show the surface of the 
water-filled soil beneath, on the date there specified, as 
determined by measurements taken at the wells indicated 
by the numbers in the figure. 

There is one marked difference between the hills and 
valleys of the water-filled soil and those of the surface 
of the ground which overlie them, and that is that the 
height of the water table is not constant. This surface 




Fig. 21. — Showing the contour of the surface of the ground. Figures 
iu the lines show height of contours above lake level; other figures 
indicate wells where the height of the water table was measured. 



o io too 20c Ft \ 

N poTA 




Fig. 22. — Showing the contour of the water table beneath the surface 
of the area represented by Fig. 21. 



166 The Soil 

rises and falls with the season, being higher usually 
in the early summer and lowest late in the winter. Its 
surface, too, in many places, tends to rise higher and 
higher when several wet seasons succeed one another, 
and then to fall with the recurrence of dry years. 

The reason why the surface of the water-filled soil is 
not level is because the soil grains offer so much resist- 
ance to the lateral flow of the water toward lakes and 
streams, that the rains which percolate beneath the sur- 
face do not have time to drain away before another rain 
comes to add its water to the soil. But if there should 
be a long term of years with little rainfall, the water 
table would sink lower and lower, and fastest where 
it is highest, until it became nearly or quite horizontal. 

When wells are sunk into the water-filled soil, it is 
evident that water may be reached at very different 
levels in different localities, and that it will not be neces- 
sary to dig to the level of some lake or stream before 
water is reached, as is commonly believed. To illus- 
trate how far this idea is from being true, it may be cited 
that a well on the campus of the University of Wiscon- 
sin has its water surface 52 feet above the level of Lake 
Mendota, only 1250 feet distant, and yet this well is dug 
all the way in a coarse sand and gravel which makes up 
the axis of an isolated glacial drumlin from 88 to 109 
feet above the surface of the lake. Now the water of 
this well owes its origin wholly to the rain which falls 
upon the hill and percolates slowly into it; and how 
slowly this may be can be understood from what has 
been cited regarding the percolation from the columns of 
sand only 8 to 10 feet long. 

In digging wells into the water-filled soil, it is evident 
that those sunk in the valleys will be less affected by 



The G-round Water and Wells. 167 

seasonal changes and will usually give a larger water 
supply, for the reason that the water under the higher 
lands tends to flow toward the valleys below ground 
just as it does above ground. Then, too, in digging 
wells, care should be taken to sink the bottom of the 
well so far below the ' level of the water table, that sea- 
sonal changes will not cause it to go dry. More than 
this, the larger the supply of water which must be 
drawn from the well, the deeper it should be sunk below 
the level of the water table, and if the well is being dug 
during the season when its natural level is highest, and 
particularly if a series of wet years have preceded the 
digging, then a special effort should be made to carry 
the bottom a considerable distance below the level at 
which water will stand in it at the time. The deeper 
the well is below the water-filled soil, the farther the 
water surface may be lowered below the level of 
the water table, and the farther the pumping carries the 
water level in the well below that of the water-filled soil, 
the faster will the water flow into the well, and the 
larger will be the amount of water it can deliver in a 
given time. 

There is another matter regarding such wells which 
should be emphasized here, and that is the danger of 
surface waters percolating into them and rendering them 
unfit for use. The soil containing only capillary water 
above the water-filled zone has in its interspaces larger 
or smaller quantities of air, so much so that all space not 
occupied with water is taken possession of by it. Now 
when heavy rains come, the surface soil is first com- 
pletely filled with water, and under these conditions it 
is at first difficult for the water to enter the soil deeply 
and also for the now confined soil air to escape. Then 



168 



The Soil 



the air, borne down by the pressure of the water above, 
has a tendency to move away in any direction where it can 



W 



^^^^^pAQjtjWtM^ : 



SP 




Fig. 23. — Showing the method of percolation of water into and out 

of wells. 

find the easiest escape, and whenever the well is not pro- 
vided with a water-tight curbing, the air tends to escape 
into the well, and then the percolating waters follow it 



The Ground Water and Wells. 169 

under the conditions represented in Fig. 23. In conse- 
quence of this tendency of both the air and the water to 
flow toward and into the well, the confined soil air forms 
a sort of broad, sloping funnel, down the sides of which 
large quantities of water from close to the surface of the 
ground are drained into the well, carrying many of the 
impurities they may have dissolved in the neighborhood. 
The sanitary aspect of this question should not be lost 
sight of; for the sudden large rise and fall of the water 
in a well associated with heavy rains is a pretty sure 
indication that that well has received surface waters, 
which, if the surroundings are bad, is liable to render 
the water unsafe to use. And observations show that 
wells in close, impervious soils are much more liable to 
surface contamination in this manner than are those in 
the more open soils, where the interspaces near the sur- 
face do not readily become closed with the fine sedi- 
ment moved by the water, as is the case with the clayey 
types. 

Just how far it is practicable to protect wells which 
are subject to contamination in this manner by using 
iron tubing or other similar impervious curbing, is a 
matter which merits careful investigation; for it is a 
vital question in the building of country homes. It is 
generally taken for granted that wells thus constructed 
are safe against the infiltration of surface water, and it 
may be true to a large extent; but it does not appear 
improbable, in pumping water from a well tubed up with 
iron, that the rapid withdrawal of water from about the 
immediate terminus of the tubing would tend quite as 
strongly to bring down a new supply from the super- 
saturated soil above, as to induce it to come from below 
or from lateral directions, and, if this is true, it is evi- 



170 The Soil. 

dent that the surface surroundings of a well used for 
domestic purposes should be scrupulously cared for, even 
when provided with impervious curbing. 

When we consider the movements to which the soil 
water is subject, it must be said that these belong to not 
less than three classes, — those due to the action of 
gravity upon the soil water direct, those due to capil- 
larity or surface tension, and again those which result 
from changes in the tension or pressure of the soil air. 

PERCOLATION MOVEMENTS OF SOIL WATER. 

The movements of the gravitational class are the most 
extensive, the most rapid, and find an expression of their 
aggregate magnitude in the vast volumes of water which 
the great rivers of the world pour into the sea. To 
appreciate the full significance of these movements of 
the ground water, we need to think of the water-satu- 
rated soil as being almost as extended and as continuous 
as the land areas of the world ; for, beneath almost every 
square foot of soil-covered surface, unless the frozen 
zones and desert regions must be excepted, there is a 
perennial percolation of water, at first downward in the 
slow fashion already referred to as taking place in the 
sand, but as the deeper, and often more porous, layers 
are reached, the movements become stronger, and finally 
the waters emerge as springs, at the foot of hillsides or 
in the bottom of lakes. 

The direction of percolation is by no means always 
downward nor even lateral. In many places it comes to 
be vertically upward, toward the surface, giving rise to 
larger or smaller areas, which require underdraining 
before they are fit for agricultural purposes. In very 



Percolation Movements of Soil Water. 171 

many localities, where a sandy or otherwise porous stra- 
tum underlies both the flat, marshy areas and the sur- 
rounding higher ground, the much greater elevation of 
the water table under the high ground causes it to act by 
direct hydrostatic pressure, to force the water to the sur- 
face on the low ground, not in the form of springs, but 
in a broad sheet which tends to keep a wide area more or 
less uniformly wet. Such areas, when they are under- 
drained, come to be the most productive lands we have, 
and largely because of the natural sub-irrigation which 
is, in such cases, taking place; and it must be remem- 
bered that lands so situated are receiving, with the 
underflow of water, not simply the lime, in the form of 
carbonates, which may have been dissolved, but also some 
of the nitrates and other soluble forms of plant food, 
which may have percolated beyond the reach of root 
action on the higher ground. 

The rate at which water percolates through soils 
varies between wide limits. In a coarse, sandy soil, 
whose grains pass a screen of 40 meshes to the inch, but 
are retained by one of 60, the writer found that water 
would percolate through a column 14 inches in length 
and .1 of a square foot in section, at the rate of 301 
inches in depth in 24 hours ; where the grains passed a 
screen of 60 meshes, but were retained by one of 80, the 
percolation was 160 inches in the same time. Reducing 
the size of the grains still further, so as to pass a screen 
of 80 meshes, but not one of 100, then the percolation 
falls to 73.2 inches in 24 hours. While sand, which 
passed a screen of 100 meshes to the inch, allowed 39.7 
inches to pass. A clay loam, on the other hand, was so 
much more impervious that only 1.6 inches passed a 
column of the same length in 24 hours, while a fine- 



172 



The Soil. 



textured black marsh soil passed only .7 inches in the 
same interval. 

Adding 20 per cent of blue clay to the sand which 
percolated 73.2 inches during 24 hours reduced the 
amount passed through it to only 10.5 inches, while 50 
per cent of clay caused a decrease to 2.7 inches during 
the same time. In all of these cases, while percolation 
was going on, the several soils were kept covered with 
water to a depth of 2 inches. 

Wollny showed, from experimental studies, that, under 
like conditions of pressure, soils having different sizes 
of grains allowed water to pass through columns 11.81 
inches deep and 1.97 inches in diameter, at the rates 
indicated below : — 

Deptii in 
Inches. 

Quartz sand .0004 to .0028 in. in diam. percolated 7.27 in 24 hours. 



Calcareous 



.0028 to .0045 " 
.0045 to .0067 " 
.0004 to .0028 " 
.0028 to .0045 " 
.0045 to .0067 " 



68.59 " " 

669.7 " " 

6.64 " " 

63.74 " " 

304.3 " " 



In these experiments of Wollny's, as in those of the 
writer, the sizes were obtained by sorting the grains 
with sieves ; but it should be observed that this method 
of separation is not very exact, as it permits varying 
amounts of grains of smaller sizes to remain among 
those having the dimensions sought, and it may be this 
fact which causes the observed differences between the 
quartz and calcareous sands. 

It must be evident therefore, from the facts here given, 
that soils differ very widely in their tendency to retain 
the rains which fall upon them, and also in their tendency 
to lose their soluble plant foods during wet periods. It 



Capillary Movements of Soil Water. 173 

is evident also that, while a small per cent of clay added 
to a sand will greatly increase its power to retain water, 
relatively large amounts of sand would have to be added 
to the stiff clays to render them very open. 

A very wrong impression would be left if it were not 
stated here that the amounts of percolation recorded 
above for the several cases are at maximum rates, and 
that such rates of percolation seldom occur in the field 
anywhere in nature. Indeed, such rates can only take 
place after all air has been expelled from the soil and the 
spaces between the grains have been completely filled 
with water. This condition rarely occurs except in the 
spring and after protracted and very heavy rains. After 
vegetation is once well under way, the surface two and 
three feet of soil are so rapidly dried that ordinary rains 
can only partially maintain such slow percolation as has 
been shown to take place from the long columns of sand 
cited above. Indeed, it more frequently happens in our 
climate, during the middle and later part of the growing 
season, that the rains we do have tend rather to strengthen 
the upward flow of water toward the surface by capillarity 
than to result in gravitational losses downward by perco- 
lation. Much the larger part of the water which goes to 
feed perennial springs is that which finds its way into 
the soil when vegetation is dormant or only feebly active: 

CAPILLARY MOVEMENTS OF SOIL WATER. 

The capillary movement of water in field soils is the 
slow creeping over the soil grains due to the action of 
surface tension, as already described. It takes place in 
any and all directions, but usually from below toward the 
surface of the ground where evaporation is taking place, 



174 The Soil. 

and toward absorbing root hairs where the surfaces of 
soil grains are being depleted of their capillary water. 

The rate at which water can be moved through soils 
by capillary action is never very rapid when compared 
with the gravitational movements we have just considered. 
It is, however, sufficiently great and extensive to be of 
the highest agricultural importance. 

When a cylinder of very fine sand, 12 inches in diame- 
ter and 4 feet high, was saturated with water and ar- 
ranged so that water could be automatically admitted to 
it from below as rapidly as it could be removed by evapo- 
ration from the surface, it was found, on placing this cyl- 
inder in a strong current of dry air, and under conditions 
where the water must be lifted 12 inches by capillarity, 
that the work of lifting was done at the mean rate of 2.37 
pounds per square foot daily during 10 days. On chang- 
ing the level of standing water in the cylinder to 2 feet 
below the surface, the mean daily capillary rise came to 
be 2.07 pounds. When the capillary lifting went on 
through 3 feet, the work done daily was at the rate of 
1.23 pounds per each square foot of surface ; while at 4 
feet it became .91 pounds. 

A similar trial with a medium clay loam gave mean 
rates of lifting water amounting to 2.05 pounds, where 
the lifting was through 1 foot, 1.62 pounds where it was 
through 2 feet, 1 pound where it was through 3 feet, and 
.9 pound where the rise was through 4 feet of this soil. 
It is very certain that the rate of capillary rise of water 
in each of these cases might have been larger had the 
evaporation from the surface been greater ; for the sur- 
face of the soil remained wet throughout all of the 
experiments. It is also certain that the decrease with the 
depth is larger than it would have been had not the de- 



Capillary Movements of Soil Water. 175 

posit of salts on the surface, tending to form a crust, 
diminished the evaporation. This fact was proven con- 
clusively in both cases by removing the crust formed on 
the surface at the close of the trials, when the mean rate 
of evaporation, and hence also of capillary rise of water 
through these soils, became 1.38 pounds for the fine sand 
and 1.27 pounds for the clay loam per square foot and 
per day. 

In another experiment, under perfectly natural field 
conditions, it was found that the surface four feet of soil 
lost, during 7 days, 9.13 pounds of water from each square 
foot of surface, and this, too, under conditions which make 
it certain that this loss was wholly due to a capillary rise 
and to evaporation from the surface. This loss gives a 
mean capillary movement amounting to 1.3 pounds daily. 
In this field case the water table was 4.5 to 5 feet below 
the surface, or rather more than in the laboratory trials 
referred to above. 

The writer has also made other field determinations of 
the capillary rise of water in field soils under field con- 
ditions, and has found, as the mean of 10 determinations 
in as many different places, a measured loss of water 
amounting to 1.65 pounds per square foot per day. In 
these trials it is quite possible that a portion of the ob- 
served loss may have been due to percolation downward. 
But, on the other hand, it should be added that it is more 
than probable that the real losses from the ground up- 
ward, and hence also the total capillary work done, were 
larger than the measured losses, because it is only fair to 
assume that capillary action was bringing water from 
below into the layers of soil, where the losses were meas- 
ured, and if this was true, such action could only tend to 
make the observed changes less than they in reality were. 



176 The Soil. 

It must not be inferred that the capillary action is uni- 
formly as rapid as the cases just cited. These should be 
looked upon, not as extremes, but as representing rates 
of movement of the soil moisture toward the surface 
which are above the average. 

"When the soil, for any reason, has become very dry, 
and also when it has been rendered loose and open so 
that it contains numerous large spaces which are many 
times the diameters of the soil grains, the rate of capil- 
lary rise of water then becomes much slower. In illus- 
tration of the slower rise of capillary water in a dry soil 
may be cited the case where cylinders of dry soil 6 inches 
in diameter and 12 inches long were placed with their 
feet standing one inch in water, under conditions where 
no evaporation could take place from their surfaces. 
Thus situated, no one of five samples was completely 
saturated at the end of 34 days. Before these soils 
appeared damp at the surface, the times given below were 
required : — 

In clay loam, time required to travel 11 inches, 6 days. 
" reddish clay " " " 

(( Ct t( (( tc u 

" clay with sand " " " 
" fine sand " " " ( 

During the first 24 days of this trial, the mean rate of 
capillary rise was .79 pounds per square foot daily, but 
when fully saturated, these soils were shown to lift the 
water at a rate exceeding 2.05 pounds per square foot 
and per day. In the case of the fine sand, the mean 
daily movement during the first 24 days was .69 pounds 
per square foot, but when fully saturated, it exceeded 2.37 
pounds, a rate more than three times as fast. 



11 


(( 


22 


11 


l< 


18 


11 


u 


6 


11 


tc 


2 



Capillary Movements of Soil Water. 177 

When the soil grains are separated from one another, 
so as to develop an open, crumbly condition, then the 
rate of capillary rise of water through it is greatly re- 
duced. Thus, plowing so thoroughly checks the loss of 
water from the soil beneath the stirred portion, that in 
one case seven very drying days failed to appreciably 
decrease the mean amount of water in the upper four 
feet of a field soil, while an immediately adjacent and 
entirely similar land, not plowed, lost, during the same 
time, the full equivalent of 1.75 inches of rain, or more 
than 9.13 pounds per square foot. So, too, in the case of 
the fine sand referred to above, while it was losing water 
at the surface at the rate of 1.38 pounds per day as a 
mean of ten days' trial, when two inches of the surface 
was removed and then laid directly back again, but in 
the loose, unflrmed condition, this treatment had the 
effect of reducing the loss of water at the surface, during 
the ten days immediately following, to a little less than 
.5 pounds per square foot daily, an amount, it will be 
seen, so small that the other rate exceeded it by more 
than 2.7 times. 

The rate, too, at which surface tension or capillarity is 
able to move water through the soil is materially influ- 
enced by the presence of various substances dissolved in 
the soil water. The writer has found that when .08 per 
cent of potassium nitrate was added to distilled water, 
which was being lifted by capillarity through columns of 
rather coarse sand 18 inches long, the rate at which the 
water passed up and away by evaporation exceeded that 
with the pure distilled water by 22.84 per cent. The 
presence of lime water, of common salt, and of sulphate 
of lime or land plaster decreased the rate at which the 
water was lifted and evaporated from the surface, while 

N 



178 



The Soil 



potassium carbonate did not appreciably affect the rate 
of movement. A saturated solution of land plaster de- 
creased the rise 27.36 per cent, while solutions of .08 per 
cent of common salt and potassium carbonate decreased 
the flow by 12.82 per cent and .66 per cent respectively. 








Fig. 24. — Showing self-recording apparatus for registering fluctua- 
tions of water in wells. 

MOVEMENTS DUE TO SOIL AIR. 

We have now to consider the movements of soil water 
due to expansions and contractions of the soil air. When 
a self-recording instrument similar to the one represented 
in Fig. 24 is placed so that its float is resting in the 



Movements Due to Soil Air. 



179 



water of a well or spring, or, if it is properly placed, in 
the water discharging from a system of tile drains, it 
will be found that the water levels in all of these cases 
are subject to numerous and sometimes very complex 
movements. So, too, this instrument, suitably placed 
upon small lakes, and even rivers, shows their surfaces 
subject to oscillations of longer and shorter periods, many 
of which are associated with changes in air pressure. 
When the barometer falls, the water in wells rises, springs 
and tile drains flow more rapidly ; but when the barom- 
eter rises again, the level of the water in wells falls, and 




Fig. 25. — Showing changes in the rate of discharge of water from a 
tile drain coincident with those of barometric pressure. The 
upper line represents the tile drain. 



springs and tile drains flow less rapidly. In Fig. 25 
will be seen the synchronous changes of the barometer 
and of the flow of water from a tile drain as they oc- 
curred during one week. 

To understand how changes in the barometer can 
affect the percolation of water into tile drains and into 
the natural waterways, it must be observed that there 
is always more or less air in the soil above the ground 
water, and that this air cannot easily and quickly 
escape, the soil offering resistance to its flow. Then, 



180 The Soil 

when the air pressure outside becomes less, this 
change is felt soonest at all natural openings to the 
ground water, such as wells, springs, and tile drains, and 
this lessening of the pressure at the outlets allows the 
water to escape more easily, and at the same time the air 
confined within the soil above the water table tends to 
expand and thus exert a downward pressure upon the 
water, tending to cause it to flow more rapidly and to 
percolate into tile drains and the natural outlets which 
lead to springs. But when the barometer rises again, 
when the air pressure becomes higher, then, as before, 
this pressure is felt first and strongest at places where 
the ground water is most exposed, and as a consequence 
some water is forced from wells back again into the soil 
which surrounds it, and the rate at which the water can 
emerge into tile drains and from the ground into springs 
is diminished for the time. These barometric changes 
have been observed to produce a change in the rate of 
flow of water from a tile drain amounting to 15 per cent, 
and in the case of a spring to 8 per cent. 

Beginning in July and extending on through Septem- 
ber, in Wisconsin, the surface of the ground water and 
the rate of percolation into tile drains are subject to 
diurnal oscillations in level and changes in the rate of 
flow which owe their origin to the daily expansion and 
contraction of air retained among the upper two to three 
feet of soil grains. The changes of pressure thus de- 
veloped react upon the capillary water of the soil in the 
zone where the cavities are nearly or quite filled, forcing 
the water down and out into drainage channels when the 
air is expanding, but allowing such as has not been 
permanently lost to return again to its normal level when 
the pressure becomes less with the cooling and contraction 



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Fig. 26. — Showing diurnal changes of the ground water under condi- 
tions represented in Fig. 27. The lower curve represents changes 
in the inner well, and the upper one in the outer well. 



182 



The Soil. 



of the soil air. In Fig. 26 are shown the diurnal changes 
here referred to as they occurred under the conditions 
represented in Fig. 27. It will be seen that the water 




vi ■:'•:'■: ^S/cmxk. 



Fig. 27. 



Showing the soil structure giving rise to the oscillations of 
ground water represented in Fig. 2(5. 



in the well rose and fell with great regularity each clay, 
and also with the slower changes of the barometer. The 
lower curve in this figure represents the changes in level 



Movements Due to Soil Air. 183 

as they occurred inside the 5-inch tile curbing in the 
centre of the main silt well, while the upper curve, where 
the diurnal changes are so pronounced, represents the 
changes in level as they occurred in the main well out- 
side of the 5-inch tile curbing. The facts are, strange 
as they may seem, that the water in the outer well os- 
cillated during the period of 20 days covered by the chart 
so as to stand, in the morning, from .1 to .3 inch above 
the level of the water in the inner one, and at night from 
.5 to 1.5 inches below that surface. To understand these 
movements, it must be observed that the well sunk in the 
centre of the larger one furnished the easiest escape for 
the water which was being lifted by the pressure of the 
surrounding higher water table under the adjacent hills, 
while vegetation in the vicinity of the well was using 
the water faster than it could percolate through the walls 
of the tile into the soil outside. On this account, and 
on account of the contraction of the air due to cooling of 
the soil, the water in the outer well fell each day, so as 
to stand below the level of the water in the inner one. 
But during the night, as the heat of the day was being 
slowly conducted downward, its expansion of the soil 
air forced out part of the water standing in the filled 
capillary spaces, until the water in the outer well rose 
from .1 to .3 inch above the water in the inner well. 
So far as the writer has observed, these diurnal changes 
due to temperature are not appreciable where the water 
table is more than 10 feet below the surface of the 
ground. 



CHAPTER VI. 

THE CONSERVATION OF SOIL MOISTURE. 

To appreciate the need of conserving the soil moisture, 
it is important to know the relation which exists between 
the amount of rain received, and the possible loss of this 
rain in ways which do not contribute to crop production. 
Now, the waters which fall as rain upon a field may be 
lost to it by running off its surface, as is too often the 
case on hilly farms ; it may be lost by percolating down- 
ward beyond the reach of root action ; or it may be lost 
by surface evaporation from the ground itself. As a 
rule, it is only that water which passes through the 
plant which materially contributes to its growth. That 
which evaporates from the surface of the soil does indi- 
rectly help the plant by leaving the food it may have 
held in solution nearer the surface of the ground, where 
it is more likely to be taken up by the roots, and in 
assisting that soil life which develops fertility. 

NEED OF CONSERVING SOIL MOISTURE. 

We have no productive lands which, under field con- 
ditions, can retain as much as 30 pounds of water to the 
100 pounds of soil, unless they lie close to or below the 
water table. In proof of this statement may be cited 
the water content of several field soils 32 hours after 
a rain of 3.19 inches which fell during 4 days. 

184 



ercu. ft. 


Per cent, 


26.79 


26.60 


26.57 


26.45 


26.45 


27.06 


25.95 


25.46 


24.76 


22.81 


24.12 


21.44 


18.00 


15.81 


18.00 


14.59 



Need of Conserving Soil Moisture. 185 

These same fields had received 3.41 inches 20 days 
earlier, and during the intervening 20 days there had 
been a rainfall of 1.3 inches. 

First Foot. Pounds. Second Foot. 
Per cent. 

No. 1, Clay soil contained 33.91 

No. 2, Clay loam " 28.88 

No. 3, Clay loam " 28.75 
No. 4, Sandy clay loam contained 26.48 

No. 5, " " " " 24.69 

No. 6, " " " " 24.61 

No. 7, Sandy loam " 17.65 

No. 8, " " " 17.65 

In these cases the clay soil will weigh about 79 pounds 
per cubic foot, the clay loams 92 pounds, the sandy clay 
loams not more than 98 pounds, and the sandy loams 
about 102 pounds per cubic foot, so that the amounts of 
water retained in the surface foot in the several cases 
were as given in the table above. 

It will be safe to say that those lands which can 
retain, in the upper five feet of soil, as much as 20 inches 
of water are very rare indeed. Then, were there no loss 
by surface evaporation nor by percolation downward, not 
more than 10 inches out of the supposed 20 inches of the 
stored water could be counted as available to a crop 
growing on the ground where large yields are expected; 
and it has been said that for lands to do their best, their 
water content should be steadily held up to from 40 to 
50 per cent of saturation, and Hellriegel says 50 to 60 
per cent. 

In stating the rate of capillary movement of water in 
field soils, as measured by surface evaporation, we have 
seen that the daily losses may be as high as 1.3 to 1.6 



186 The Soil. 

pounds per square foot. On well-tilled, fallow ground, 
too, we have observed a mean loss of water amounting to 
.67 pounds per square foot, during a period of 64 sum- 
mer days, which is equivalent to 8.24 inches. If we 
take the average daily loss from the soil at only .25 
pounds per square foot, from May 1 to Sept. 1, this 
would be equivalent to 5.77 inches of rain, and deduct- 
ing this from a mean rainfall of 12 inches for the same 
period, we should have left 6.23 inches for the use of a 
field crop, which, added to the 10 inches we have sup- 
posed might be withdrawn from that stored in the upper 
five feet of soil, gives a total for crop production of 16.23 
inches. 

Were it possible to have 16 inches of water to the acre 
for crop production, over and above losses by percolation 
and evaporation from the soil surface, large yields, so 
far as water contributes to them, would be certain, — 
yields amounting to from 3.5 to 7 tons of dry matter to 
the acre. In our experiments, where we have attempted 
to measure the water used in the production of a ton of 
dry matter, our smallest yield has been at the rate of 4 
tons, and our largest at the rate of 17 tons, with an 
average for 22 cases of over 7 tons of dry matter per 
acre. In all of these trials, however, whether with 
oats, barley, corn, peas, clover, or potatoes, water was 
so added to the soil, from time to time, as to maintain 
for it a constant saturation of 40 to 50 per cent. Now, 
since ordinarily fertile lands, when well watered, will 
yield such large returns, and since it is seldom true that 
16 inches of water are available for the use of crops 
under natural conditions, it follows that by whatever 
means we can diminish the loss of water from the soil, 
or render a larger per cent of it available to the crops 



Saving Soil Moisture by Plowing. 187 

growing upon it, their adoption may reasonably be 
expected to give larger yields. What, then, may be done 
to conserve soil moisture? 



SAVING SOIL MOISTURE BY PLOWING. 

Plowing land in the fall has a very appreciable influ- 
ence on the per cent of water the surface three or four 
feet of such soil may contain the following spring, and 
the writer has observed a mean difference of 2.31 per 
cent more water in the upper three feet of immediately 
adjacent lands plowed late in the fall, as compared 
with that not plowed, the surface of neither having been 
disturbed until May 14. The larger quantity of water in 
the fall-plowed ground, in this case amounting to not 
less than 6 pounds to the square foot, was due partly to 
two causes; namely, the loose, open character of the 
overturned soil, causing it to act as a mulch during the 
fall, and again in the spring, after the snows had disap- 
peared; and the more uneven surface, which tended to 
permit more of the melting snow and early spring rains 
to percolate into the soil. 

Late fall plowing, leaving the surface uneven and 
the furrows in such a direction as to diminish washing, 
works in a decided manner, on rolling land, to hold the 
winter snows and rains where they fall, giving to such 
fields a more even distribution of soil water in the spring. 
And when it is observed that heavy lands, after a dry 
season, seldom become fully saturated with water during 
the winter and spring, the importance of fall plowing 
in such cases can be appreciated. 

From the standpoint of large crops, which result from 
the best use of the soil moisture, there is no one thing 



188 The Soil. 

more important for a farmer to strive for than the earli- 
est possible stirring of the soil in the spring, after it 
has sufficiently dried so as not to suffer in texture from 
puddling. When the soil is wet, when its texture is 
close from the packing which has resulted from the 
winter snows and early spring rains, the loss of water is 
very rapid, as has been pointed out ; it may be more than 
20 tons daily per acre, and this loss may extend to depths 
exceeding four feet. 

We must give here the details of an experiment aim- 
ing to measure the influence of early spring plowing 
on the loss of water from the soil, some of the results 
of which have already been referred to. 

On April 28, a piece of corn ground was plowed and 
sowed to oats, and on the next day samples of soil were 
taken, in one-foot sections, down to a depth of four feet. 
Seven days later samples of soil were again taken, and 
below are given the percentages of water as they were 
found on the two dates. 

1st Foot. 2d Foot. 3d Foot. 4th Foot. 

Per cent. Per cent. Per cent. Per cent. 

Water in soil April 29 20.13 22.01 20.51 17.72 

Water in soil May 6 19.80 23.24 20.80 17.17 

Difference, -.27 +.03 +.35 -.55 

It is thus seen that there had been little change in 
the water content of the soil during the week, the 
capillary movement upward nearly keeping pace with 
the loss by surface evaporation. Adjoining this piece 
and separated from it by a strip of grass only 10 feet 
wide, lay another piece of ground which was not plowed 
until May 6, and on this date, before plowing, samples 
of soil were taken from it in the manner already de- 



Saving Soil Moisture by Plowing. 189 

scribed, and below are given the amount of water which 
this unplowed land contained, and with these, for com- 
parison, the amounts which were found in the piece 
which had been plowed seven days earlier. 





1st Foot. 


2d Foot. 


3d Foot. 


4th Foot. 




Lbs. Water. 


Lbs. Water. 


Lbs. Water. 


Lbs. Water. 


Land plowed 


13.87 


20.66 


18.32 


16.05 


Land not plowed 


10.58 


17.98 


17.28 
1.05 


13.91 


Loss 


3.29 


2.68 


2.11 



It is thus seen that the unplowed ground had lost, 
during the seven days, in consequence of not having been 
plowed, not less than 9.13 pounds of water per square 
foot more than the plowed ground had, an amount 
equivalent to 1.75 inches of rain, and more than 198 tons 
of water per acre ; and it should be said in this connection 
that there can be no reasonable doubt but that the actual 
loss was greater than this, because there must have been, 
during all this time, a movement of water upward from 
below the level at which the samples were taken into 
the four feet above, and whatever this movement may 
have been, it by so much diminished the observed losses. 

There was another very serious result which followed 
this delay in plowing, for there were developed in the 
unplowed ground, as a consequence of the rapid loss of 
water from the soil, great numbers of very large and 
hard clods. So that, instead of having this piece of land 
in excellent tilth with plowing and once harrowing, it 
became necessary to go over the ground twice with a 
loaded harrow, twice with a disk harrow, and twice with 
a heavy roller, before it was brought into a condition of 
tilth even approximating what it might have had had it 
been plowed seven days earlier. 



190 The Soil. 

It follows from these observations that all lands, with 
but few exceptions, should be tilled at as early a date 
in the spring as their condition of moisture will permit, 
and not simply to save the all-important soil moisture 
and the formation of clods, but for other and very weighty 
reasons which will be stated in another place. 

EARLY SEEDING AND CATCH CROPS. 

The farmer who gets his crop to growing upon the 
ground at as early a date as the temperature of the air 
and of the soil will permit, is conserving soil moisture 
in still another way ; for so soon as a crop gets possession 
of the land, so soon does it begin to use the water which 
is certainly running to waste upward, and possibly also 
downward; and more than this, the farmer who fails to 
give his crop possession of the land as soon as the 
season will permit, fails to get full advantage from the 
sheltering of the ground by the plants, and the dimin- 
ished surface evaporation which results from the drying 
« action of the crop. On all soils which do not have a 
strong tendency to run together after heavy rains, as a 
consequence of working, early surface tillage may often 
be adopted with great advantage even when the crops, 
like corn and potatoes, are not to be put in until late ; 
a richer seed bed in better tilth, with more moisture and 
fewer weeds, being among the gains. 

Where fields are naked through the winter, there is 
necessarily a large waste of moisture from the melt- 
ing snows and earliest spring rains, which is often 
worse than a dead loss, because, so far as these waters 
drain away downward, they carry with them, and often 
beyond recovery, considerable amounts of nitrates and 



Early Seeding and Catch Crops. 191 

other valuable soluble and immediately available forms 
of plant food. Now, it is a matter worthy of serious 
consideration in studying this problem of conservation 
of soil moisture, whether it is not best in most cases of 
fall plowing to have some catch crop on the ground for 
the express purpose of utilizing the excess of moisture in 
the spring, which must be allowed to drain away or to 
evaporate before the ground is in condition to work. 
With the catch cro}), the ground is dried earlier, and 
the moisture turned to account in preventing loss of fer- 
tility by drainage. 

In the use of catch crops for this purpose, as in all 
cases of green-manuring, great judgment must always be 
exercised in order not to allow them to remain so Ions 
upon the ground as to so thoroughly exhaust the stock 
of soil moisture that the main crop is placed at a disad- 
vantage on this account. In illustration of this danger, 
and as serving to enforce the great importance of keep- 
ing all fields free from weeds, an observation on the dry- 
ing effect of clover will be instructive. 

On May 13, the water content of soil in a field just 
planted to corn, and in a field of clover adjacent to it, 
was determined, the two sets of samples being taken 
within less than two rods of each other. The differ- 
ences in the amount of water in the two cases were as 



given below. 

Corn ground 
Clover ground 


1 to 6 Inches. 
Per cent. 
23.33 
9.59 


12 


to 18 Inches. 
Per cent. 

19.13 

14.75 


18 


to 24 Inches. 
Per cent. 
16.85 
13.75 


Difference 


13.74 


4.38 


3.10 



We have here a very forcible illustration of the danger 
of using catch crops, and of the evil consequences of 



192 The Soil. 

allowing a field, when occupied with another crop, to 
become encumbered with weeds. In the case of the 
weeds, the soil is not only robbed of its moisture, but 
soluble plant food is also locked up in the tissues of the 
weed, in a form in which it is not immediately available. 
Had the clover field been plowed a week earlier than 
the samples were taken, it is quite likely that even then 
so much moisture had already been used that not enough 
remained to quickly decompose the material turned 
under, and at the same time meet the needs of the crop 
put upon the ground. 

In plowing under coarse herbage, too, when the soil 
has a scanty supply of moisture, it is very difficult to 
establish such a capillary connection with the soil 
below as will allow a sufficient amount of water to rise 
into the overturned portion to start and properly feed a 
crop. 



CULTIVATING AND HARROWING. 

In the conservation of soil moisture by tillage, there 
is no way of developing a mulch more effective than that 
which is produced by a tool working in the manner of 
the plow, to completely remove a layer of soil and lay 
it down again, bottom up, in a loose, open condition. 
The harrow, when it scratches or cuts the surface of a 
field, without completely covering it with a layer of 
loose crumbs, hastens rather than retards the loss of 
moisture from the soil. So, too, when a tool is used 
which plows deep and wide grooves, leaving untouched 
and only partly covered ridges between them, it increases 
instead of lessening the rate of evaporation. That most 



Cultivating and Harrowing. 193 

excellent tool, the disk harrow, may be used so as either 
to hasten or check the loss of moisture from the soil, 
according as its disks are set at a very small or a large 
angle. In one trial, the writer increased the rate of 
evaporation from the surface of a 12- inch cylinder of 
soil from .75 pounds per square foot in 24 hours to 1.38 
pounds in the same time by simply making vertical cross- 
cuts in the surface with a sharp knife; but when a whole 
layer was removed in the fashion of the plow, and 
replaced in the loose condition, the rate of loss was then 
reduced to .5 pounds. When a strip of land is culti- 
vated to a depth of 3 inches frequently during a whole 
season, while an adjacent strip is left smooth and 
unstirred, both pieces being fallow and kept free from 
weeds, the difference in the amount of moisture in the 
soil becomes very appreciable. In a test of this sort, /^ 
where the amount of water in the soil was determined 
in one-foot sections to a depth of 6 feet, the mean daily 
loss per acre was at the rate of 14.48 tons on the culti- 
vated ground, and 17.6 tons on the ground not cultivated, 
and these amounts are over and above what may have c^ 
been brought up into the 6 feet by capillary action from 
below, and are the averages for 49 days. This repre- 
sents a saving of water in that time equivalent to 1.7 
inches of rainfall. 

When stirring the soil to a depth of 3 inches is com- 
pared with that of 1 to 1.5 inches, the 3-inch mulch is 
decidedly more effective, so far as its conserving soil 
moisture is concerned. Through extended and repeated 
field trials, on different soils and in different seasons, 
the writer has found that invariably there is left at the 
end of the season a larger amount of water in the soil 
where it is stirred to a depth of 3 inches than when 



194 



The Soil. 



stirred to a depth less than this amount. The observed 
differences in a field of corn for one season are given 
below. 





1st Foot. 
Per cent. 


2d Foot. 
Per cent. 


3d Foot. 
Per cent. 


4tii Foot. 
Per cent. 


Cultivated 3 inches deep 
Cultivated 1 inch deep . 


23.14 
22.70 


23.30 

21.08 


21.94 
19.65 


22.46 

19.58 


Difference . . . 


.44 


2.22 


2.29 


2.88 



These differences at the end of the growing season, 
represent 167.4 tons more water per acre in favor of the 
deeper mulch. 



SOIL MULCHES. 

When the effectiveness of very thin soil mulches is 
measured, it is found that here, too, the lessening of the 
rate of evaporation may be very considerable. Thus 
it was found, by laboratory methods, that when the 
evaporation from an unstirred surface was at the rate of 
6.24 tons per acre daily, from the same surface, when 
stirred to a depth of .5 inch and .75 inch, the loss 
was only 5.73 tons and 4.52 tons respectively. Again, 
when the surfaces were covered with a fine, dry clay 
loam to a depth of .5 inch and .75 inch, the daily loss 
was then at the rate of 6.33 tons per acre per day for 
the naked surface, but only 4.54 tons and 2.4 tons for the 
mulches, respectively. 

There is thus left no room to doubt the efficacy of dry 
earth mulches as conservators of soil moisture, but it 



Translocation of Soil Moisture. 195 

should be said that not all soils are equally effective in 
their power to diminish evaporation. 

The writer has found that, taking the evaporation 
through a mulch of 2 inches of dry quartz sand, which 
passes a screen of 20 meshes, but is retained by one of 
40 meshes to the inch, as 1, the rate of evaporation 
through the same depth of finely pulverized, air-dry clay 
loam was 3.5 times more rapid ; the latter giving, in the 
still air of the laboratory, a loss of 3.474 inches in depth 
per 100 days, while the loss through the sand was .995 
inch in the same time. This difference in the effective- 
ness of the two soils to act as mulches depends appar- 
ently upon the difference in their capillary power, the 
fine soil with its small pores, even when air-dry, lifting 
the water faster than the sand. 

It is to be observed, further, that the mulching effect 
of a soil decreases with time, the capillary power becom- 
ing stronger as the per cent of water in the mulch 
increases. Experiments showed that the coarse sand 
referred to above, which had been allowing water to pass 
through it during 30 days at the mean rate of .027 inch, 
decreased the rate to .0099 inch when a fresh mulch 
was substituted. So, too, in the case of the fine clay the 
rate of evaporation decreased from a mean daily loss of 
.071 inch to .034 inch when the old mulch was re- 
placed by the fresh. It follows, therefore, that to main- 
tain the most effective mulches in the field requires 
frequent stirring, even though a rain may not have 
occurred to pack the soil. 

TRANSLOCATION OF SOIL MOISTURE. 

When a surface soil has its water content reduced, so 
that the upper 6 to 12 inches is beginning to be dry, the 



196 The Soil. 

rate of capillary rise of water through it is decreased and 
it begins to assume the properties of a mulch. But 
when this condition has been reached, if a rain increases 
the thickness of the water film on the soil grains with- 
out causing percolation, the capillary flow may be so 
strengthened that the surface foot draws upon the deeper 
soil moisture at a more rapid rate than before, causing a 
translocation of the lower soil moisture, the deeper soil 
becoming measurably drier soon after such a rain than it 
was before it, while the surface foot is found to contain 
more water than has fallen upon it. 

The following experiment may be cited in proof of 
this important principle. At 5.30 p.m. samples of soil 
were taken on a piece of fallow ground in one-foot sec- 
tions to a depth of four feet. Water was then applied 
to this surface at the rate of 1.33 pounds per square foot. 
Samples of soil were also taken adjacent to this wetted 
area to serve as a control experiment, and 19 hours later 
corresponding sets of samples were again taken with the 
results stated below. 

POUNDS OF WATER PER CUBIC FEET OF WET AREA. 

Before wetting 
After wetting 

Gain 2.28 1.73 .85 1.43 

POUNDS OF WATER PER CUBIC FOOT OF AREA NOT WET. 

1st Foot. 2d Foot. 3d Foot. 4tii Foot. 
First samples 12.38 17.05 14.92 14.48 

Second samples 12.75 17.72 15.40 14.17 

Gain .37 .67 .48 -.31 

Now, it will be seen from these results that the water 
content of the soil increased on both areas, but at the 



1st Foot. 


2d Foot. 


3d Foot. 


4th Foot. 


11.78 


15.79 


14.73 


14.03 


14.06 


17.52 


15.58 


15.40 



Translocation of Soil Moisture. 197 

rate of 6.23 pounds per square foot on the wet area, 
and 1.21 pounds on the area not wet. The 19 hours 
which intervened between the taking of the two sets of 
samples was a period of very little evaporation, most of 
it being in the night, and the following morning was 
cloudy and very damp, and the result was that capil- 
larity gave to the area not wet 1.21 pounds more water 
per square foot than it lost by evaporation. But the wet 
area had gained 6.23 pounds, and yet only 1.33 pounds 
had been added to the surface, making the increase by 
capillarity 



6.23 - 1.33 = 4.90 lbs. 



and if we subtract from this the amount which the con- 
trol area gained, we shall have 3.69 pounds as the water 
of translocation due to the wetting of the surface. 

This is not an isolated observation ; for the experiment 
was twice repeated, and the fact had been several times 
observed in the field when taking samples of soil just 
before and again immediately after rains, these observa- 
tions leading to making the experiments. 

Now, when it is recognized that rains which do not 
cause percolation tend to strengthen the flow of the 
deeper soil water toward the surface, while they have at 
the same time greatly diminished the power of this soil 
to act as a mulch, it should be very evident that, at criti- 
cal times like these, no time should be lost in developing 
a new mulch which shall retain in the upper soil, not 
simply the rain which has fallen, but the moisture it has 
caused to be brought up from below; for if this is not 
done, the ground as a whole will have become drier in a 
few days than it would have been had no rain fallen. 



198 The Soil 

It will often happen in farm practice, after a field of 
corn or of potatoes has been laid by in perfect condition, 
so far as being free from weeds and in possessing a good 
mulch are concerned, that a rain may come, making it 
advisable to cultivate the field once more in order to 
restore the mulch, and to retain the water which trans- 
location has brought up within the reach of root action. 

It will be evident also that when watering transplanted 
trees or other plants, during a dry time, care should be 
taken to add water enough to produce percolation, and 
then to protect the wet surface with some sort of mulch ; 
for unless this is done, the chances are that more harm 
than good will result. It is evident, too, from what has 
been said regarding mulches, that transplanted trees 
should be early protected by an ample mulch and by 
keeping the ground above and near the roots entirely free 
from grass and weeds, whose power to withdraw water 
from a dry soil far exceeds that of the pruned and muti- 
lated roots of transplanted trees. 

There is another effect resulting from the transloca- 
tion of soil moisture, as influenced by cultivation and 
the use of mulches in other ways, which is very impor- 
tant in the saving and utilization of the water deep in 
the ground. It is in the upper 18 inches of soil that 
the nitrates are developed through the processes of 
nitrification, and it is from here, too, that plants must 
obtain them. To the upper soil also other fertilizers are 
applied, and from it these must be removed, and it can 
only be done when water enough is present to allow the 
processes of diffusion to be carried forward. 

Now, keeping the upper 18 inches of soil sufficiently 
moist enables the process of translocation to bring into 
use a larger amount of the water deep in the ground ; 



Translo cation of Soil Moisture. 



199 



that is, to lift it into the zone of soil near the surface, 
where, through a more plentiful supply of air, carbon 
dioxide and the presence of micro-organisms, it is far 
more serviceable in preparing and giving to the plant 
the food it needs than it could be if absorbed by the 
roots at a lower level in the ground. 

That a sufficiently deep mulch, prepared by cultivation, 
does act in this manner is proved by the observed dis- 
tribution of water in the soil when cultivated deep and 
shallow and when cultivated and left unstirred. In 
both of these classes of cases the writer has repeatedly 
observed at a certain stage in the drying of field soils 
that, while the surface two or three feet of the better 
mulched soil will contain more water than the corre- 
sponding layer of the unmulched or poorly mulched soil, 
the third and fourth or the fifth and sixth feet may be 
wetter beneath, where the surface has been least protected. 

On three different fields of corn, with as many different 
kinds of soil, where the ground was cultivated 3 inches 
and 1.5 inches deep respectively, the writer found on 
July 16, 1894, the following distribution of soil moisture. 





1st Foot. 
Per cent. 


2d Foot. 
Per cent. 


3d Foot. 
Per cent. 


4th Foot. 
Per cent. 


No. 1, cultivated 3 inches 
No. 1, " 1.5 " 


11.30 
9.92 


15.57 
15.43 


10.54 
11.56 


11.37 
13.99 


Difference, 

No. 2, cultivated 3 " 
No. 2, " 1.5 " 


+ 1.38 
13.96 
12.98 


+ .14 

22.74 
20.44 


-1.02 

23.39 
24.02 


-1.62 

19.47 
21.34 


Difference, 

No. 3, cultivated 3 " 
No. 3, " 1.5 " 


+ .98 

11.65 
10.65 


+ 2.30 

17.47 

16.85 


-.63 
16.44 
17.81 


-1.87 
13.03 
13.32 


Difference, 


+ 1.00 


+ .62 


-1.37 


-.29 



200 The Soil. 

Differences similar to these were obtained in cornfields 
in 1893 and also on fallow ground, where the rates of 
evaporation on cultivated and uncultivated soil were 
compared, and that these differences are effective in crop 
production is borne out by the fact that in fifteen trials 
out of twenty the yield of corn was larger on land culti- 
vated 3 inches deep than it was on land cultivated only 
1.5 inches deep. The facts appear to be that wherever 
we can succeed in holding the per cent of water relatively 
high in the surface two feet, a larger per cent of the 
water in the next four feet at least becomes available 
and is actually brought nearer the surface, where it has 
the highest value in crop production ; and then, if what 
has been said is true, it follows that less water and less 
fertility are lost by percolation. 

EFFECT OF ROLLING ON SOIL MOISTURE. 

It used to be generally believed by farmers, and per- 
haps the majority of them still have the impression, 
that firming the surface of the ground, as with the roller 
or with the wheels of the press drill, increases the water 
content of the soil ; and that this belief should have 
been so generally entertained is what would be expected 
from the very evident fact that firming the surface of 
the ground does, for the time, increase the amount of 
water in the compacted portion. 

When, however, the changes in the water content of 
the surface four feet of soil which follow the use of a 
heavy roller are studied, it is found that we have here 
another case of the translocation of soil moisture ; a 
case where, by destroying the many large non-capillary 
pores in the soil and bringing its grains more closely 



Effect of Rollhig on Soil Moisture. 201 

together, its water-lifting power is increased and to such 
an extent that often within 24 hours after rolling, the 
upper one or two feet of the firmed ground have come to 
contain more moisture than similar and immediately 
adjacent land does at the same level, while the lower 
two feet have become drier. Water has been lifted from 
the lower into the upper soil. 

In the table below will be seen the difference in the 
water content of the soils which have been rolled, and 
immediately adjacent ones not so treated. These results 
are averages derived from 147 pairs of samples. 

Surface 36 to 54 inches, unrolled 19.43 per cent. 



(( 


36 to 54 


tc 


rolled 


18.72 


u 








difference 


- .71 


u 


cc 


24 


u 


unrolled 


19.85 


(( 


(( 


24 


u 


rolled 


19.49 


it 








difference 


-.36 


a 


(« 


2 to 18 


K 


unrolled 


15.64 


u 


(( 


2 to 18 


(( 


rolled 


15.85 


u 



difference + .21 " » 

It is here seen that when samples are taken to a depth 
exceeding two feet, the rolled ground as a whole is drier 
than that not rolled, and that this difference is greater 
when the samples are taken to depths of from three to 
four or more feet. The data presented also show that 
the surface 2 to 18 inches of loose ground recently firmed 
contains more water than that which has not been so 
treated. 

While firming loose soil tends, therefore, at first, to 
increase the moisture in the surface soil at the expense of 
the deeper layers, the whole ground soon comes to con- 
tain less, on account of an increased rate of evaporation. 



202 The Soil 

It is not simply because the water is brought to the 
surface by firming that a more rapid loss of water takes 
place after rolling, but making the ground very smooth 
increases the wind velocity close to the surface, and to 
such an extent that it may exceed that on the unrolled 
ground by more than 70 per cent. It is plain, therefore, 
that whenever it becomes desirable to firm the surface 
for the purpose of increasing the amount of water in it, 
a light harrow should follow the roller in order to restore 
a thin mulch which shall retain the water brought up 
by the firming ; for unless it is done, only a temporary 
advantage is derived from it. 

It sometimes occurs, after sowing spring grain, that 
heavy rains develop a crust, which diminishes the poros- 
ity of the soil beyond what is most desirable. When 
this has taken place, and if the surface is uneven, owing 
to harrow ridges and numerous lumps, then, by using the 
roller when the ground is dry, the crust and the lumps 
may be crushed and a partial mulch formed, while at 
the same, time the porosity of the surface will be to 
some extent restored. 

DEEP TILLAGE AND LEVEL CULTURE. 

In the conservation of rains in regions where they are 
scanty and where surface evaporation is very rapid, it 
may sometimes be desirable to work the soil unusually 
deep in order to insure a deeper percolation of water 
into the ground and a slower return of it to the surface. 
Deep Avorking, through the formation of numerous non- 
capillary spaces, increases the rate of percolation and at 
the same time decreases the capillary return to the sur- 
face ; so that in climates where so little water falls that 



Deep Tillage and Level Culture. 203 

only a small amount ever drains away, methods of tillage 
may be desirable which in humid regions would not be 
prudent. In regions of large rainfall, at times when 
fields are not bearing crops, the great danger lies in the 
loss of fertility through excessive percolation ; so that in 
such countries and at such times a rapid evaporation of 
soil moisture is to be encouraged. 

Ample root room is a very necessary condition for the 
largest utilization of soil moisture. When, for any rea- 
son, the roots of plants are forced to develop close to or 
near the surface of the ground, as is the case when a 
field is insufficiently underdrained, then, as the plants 
approach the fruiting stage and begin to use water very 
rapidly, the zone of soil in which the roots lie is so 
rapidly depleted of its moisture that capillarity is unable 
to prevent it from becoming dry, and the result is that 
a large amount of moisture near at hand becomes unavail- 
able, when, if the water table in the early part of the 
season had occupied a lower level, the roots would have 
developed more deeply, and they could have come into near 
contact with a larger volume of soil and of water. Then 
by taking water at a relatively slower rate and from a 
greater depth, a strong capillary flow upward is longer 
maintained and from lower levels in the ground, so that a 
much larger amount of the soil moisture becomes available. 

Then, too, those methods of tillage which leave the 
surface of the field nearly flat rather than thrown up 
into ridges and hills are less wasteful of soil moisture. 
To hill potatoes or corn to a height of 6 inches when the 
rows are 3 feet apart may increase the surface ex- 
posed to the sun and evaporation more than 5 per cent, 
and if ridged to a height of 9 inches more than 9 per 
cent. Under these conditions the water must rise to a 



204 The Soil. 

greater height under the rows before reaching the sur- 
face roots, while midway between them and where the 
ground is least shaded, the unmulched surface lies near- 
est the water supply. These being the conditions, ridge 
culture must be more wasteful of soil water than level 
tillage, whence it becomes evident that naturally dry 
soils everywhere, and most soils in dry climates, should, 
wherever practicable, be given flat cultivation. 

On stiff, heavy soils in wet climates and during wet 
seasons it may become desirable to practice ridge culture 
with potatoes and some of the root crops, but not so 
much to increase the rate of evaporation from the soil 
as to provide a soil bed in which it will be less difficult 
for fleshy tubers and roots which form beneath the sur- 
face to expand. A clay soil, after having been thor- 
oughly wet and then allowed to dry, shrinks into so 
firm a mass that it is very difficult for potatoes to ex- 
pand in it; and under these conditions they tend to 
form at or above the surface. Hilling in such cases is 
very beneficial, although more wasteful of soil moisture. 

DESTRUCTIVE EFFECT OF WINDS. 

In arid or semiarid countries and in districts where 
the soil is light and leachy, but especially where there 
are large tracts of land whose incoherent soils suffer 
from the drifting action of winds, it is important that 
the velocity of the winds near the ground should be 
reduced to the minimum. We have in Wisconsin exten- 
sive areas of light lands which are now being developed 
for purposes of potato culture ; but while these lands are 
giving fair yields of potatoes of good quality, they are 
in many places suffering great injury from the destructive 



Destructive Effect of Winds. 205 

effects of winds. On these lands, wherever broad, open 
helds lie unprotected by windbreaks of any sort, the 
clearing west and northwest winds after storms often 
sweep entirely away crops of grain after they are 4 
inches high, uncovering the roots by the removal of 
from 1 to 3 inches of the surface soil. It has been 
observed, however, that such slight barriers as fences 
and even fields of grass afford a marked protection 
against drifting for several hundred feet to the leeward 
of them. 

In the case of groves, hedgerows, and fields of grass, 
their protection results partly through their tendency 
to render the air which passes across them cooler and 
more moist, and partly by diminishing the surface veloc- 
ity of the wind. The writer has observed that when the 
rate of evaporation at 20, 40, and 60 feet to the leeward 
of a grove of black oak 15 to 20 feet high was 11.5 cc, 
11.6 cc, and 11.9 cc, respectively, from a wet surface of 
27 square inches, it was 14.5, 14.2, and 14.7 at 280, 300, 
and 320 feet distance, or 24 per cent greater at the three 
outer stations than at the nearer ones. So, too, a scanty 
hedgerow produced observed differences in the rate of 
evaporation, as follows, during an interval of one hour : — 

At 20 feet from the hedgerow the evaporation was 10.3 cc. 
At 150 " " " " " " " 12.5 cc. 

At 300 " " " " " " " 13.4 cc. 

Here the drying effect of the wind at 300 feet was 30 
per cent greater than at 20 feet, and 7 per cent greater 
than at 150 feet from the hedge. 

When the air came across a clover field 780 feet wide, 
the observed rates of evaporation were, — 



206 The Soil. 

At 20 feet from clover, 9.3 cc. 
At 150 " " " 12.1 cc. 

At 300 " " " 13.0 cc. 

or 40 per cent greater at 300 feet away than at 20 feet, 
and 7.4 per cent greater than at 150 feet. 

The protective influence of grass lands and the dis- 
advantage of very broad helds of these light soils was 
further shown by the increasingly poorer stand of young 
clover as the eastern margin of these fields was ap- 
proached, even on fields where the drifting had been 
inappreciable. Below are given the number of clover 
plants per equal areas on three different farms, as the dis- 
tance to the eastward of grass fields increased : — 

No. 1, at 50 feet, 574 plants ; at 200 feet, 390 plants ; at 400 feet, 
231 plants. 

No. 2, at 100 feet, 249 plants ; at 200 feet, 277 plants ; at 400 
feet, 193 plants ; at 600 feet, 189 plants ; at 800 feet, 138 plants ; 
at 1000 feet, 48 plants. 

No. 3, at 50 feet, 1130 plants ; at 400 feet, 600 plants ; at 700 
feet, 543 plants. 

In these cases the difference in stand appears to have 
resulted from an increasing drying action of the wind. 
On the majority of fields the destructive effects of the 
winds were very evident to the eye, and augmented as 
the distance from the windbreaks increased. 

It appears from these observations, and from the pro- 
tection against drifting which is afforded by grass fields, 
hedgerows, and groves, that a system of rotation should 
be followed on such lands, which avoids broad, continuous 
fields. The fields should be laid out in narrow lands and 
alternate ones kept in clover and grass. Windbreaks of 
suitable trees must also have a beneficial effect when 
maintained in narrow belts along line fences and rail- 
roads and perhaps wagon roads, in places. 



CHAPTER VII. 

THE DISTRIBUTION OF ROOTS IN THE SOIL. 

When we look at the habit of growth among higher 
plants, it is to be noted that, excepting a few very consoli- 
dated forms of vegetation like the cacti, whose natural 
habitat is in arid or semiarid regions, plants spread out in 
the air and in the soil two very broad surfaces joined by 
a relatively narrow and rigid stem. The roots, branching 
in the ground, dividing and subdividing until numberless 
root hairs have threaded themselves through the capil- 
lary spaces among the soil grains, are there to gather 
water, nitrogen, and ash ingredients for growth. So large 
is the quantity of water demanded by plants, so small is 
the amount of water within a small area of soil, and so 
slow is the method by which the roots obtain it, that 
nothing short of an enormous root surface could do the 
work, and how great this surface really is may be par- 
tially appreciated from the photo-engraving of the roots 
of corn, clover, oats, and barley shown in Fig. 28. These 
roots were obtained by growing the plants in a deep cylin- 
der holding between 500 and 600 pounds of earth and 
then, at maturity, carefully washing the soil away with 
a fine stream of water. 

THE NEED AND GREAT EXTENT OF ROOT SURFACE. 

That we may the more clearly appreciate the great 
need there is for the vast extent of root surface spread 

207 



208 



The Soil. 



out by agricultural crops, and how important it is that 
there shall be a deep, well-drained, and well-tilled soil 
in which they may expand, let me give the measured 
amounts of water used by four stalks of corn and with- 
drawn by their roots from the soil between July 29 and 
August 11. Two stalks of maize were growing in each of 




Fig. 28. — Showing the total root of four stalks of maize, and of oats, 

clover, and barley. 

two cylinders filled with soil, having a depth of 42 and a 
diameter of 18 inches. These four stalks of corn, as they 
were coming into tassel and their ears were forming, used 
during 13 days 150.6 pounds of water, or at the mean 
daily rate of 2.896 pounds for each stalk. Had an acre 
of ground been planted to corn in rows 3 feet 8 inches 
each way and four stalks in a hill, then, with an average 



Need and Great Extent of Root Surface. 209 

consumption of water at the observed rate given above, 
there would have been withdrawn from that acre an 
amount of water during those 13 days equal to 244 tons 
or 2.42 acre-inches ; and when it is observed that this 
must be withdrawn from a soil so dry that no amount of 
pressure could express from it a drop of water, it is not 




Fig. 29. — Showing the natural distribution of corn roots in a field soil 
under natural conditions. 

strange that a mass of roots like those shown in Fig. 28 
should be required to do the work with sufficient rapidity. 
Referring now to Fig. 29, it will be seen how completely 
the whole soil of the field is threaded with roots ; for in 
both cases two hills of corn, standing opposite each other 
in adjacent rows, are shown and the roots meet and pass 
one another between the hills, and in the younger stage 



210 The Soil. 

these had already exceeded a depth of two feet, while in 
the second case, taken just as the corn was coming into 
tassel, the roots had descended until at this time the 
whole upper three feet of the field soil appeared to 
be so fully occupied with corn roots that not a cube of 
earth one inch on a side existed in the three feet of depth 
which was not penetrated by more than one fibre of 
thread-like size. In many portions of the soil the roots 
were much closer than this, and the minute root hairs 
which branch out from the thread-like fibres referred to, 
and which constitute the chief absorbing surfaces of the 
roots, are not included in making this statement of root 
occupancy. 

At the distance apart of planting in the field from 
which these roots were taken, there were in the surface 
three feet 40J cubic feet of soil available for each four 
stalks, so by multiplying the 1728 cubic inches in one 
cubic foot by 40^, the number of cubic feet of soil occu- 
pied, we get a total of 69,696 cubic inches. If, then, each 
cubic inch of this soil contains not less than one linear 
inch of thread-like root, their aggregate length could not 
be less than one-twelfth of 69,696, or 5808 feet, which is 
just 1.1 miles. 

Let the reader keep in mind that the corn roots here 
under consideration grew in the field under perfectly 
natural conditions, and that the cage of wire shown in 
the engraving was simply slipped over the block of soil 
which contained the roots there shown, after the corn had 
reached the stage of maturity represented in the figure. 
It should also be understood that the four stalks of corn 
which drank the 150.6 pounds of water in 13 days, 
did it at the stage of growth represented by the oldest 
plants in Fig. 29 ; and, further, that these stalks were 



Need and Great Extent of Root Surface. 211 

only good average plants, such as would make a yield of 
4.5 tons of dry matter per acre. 

Is this not a sublime expression of one of nature's 
methods of utilizing all her opportunities and making 
the most out of whatever is at hand ? The rocks had 
fallen into decay, the sun warmed the bed of incoherent 
fragments, the winds had brought the rains, capillarity 
had retained a portion of them on the surfaces of the 
soil grains, the forces of solution had charged these 
waters with plant food, but roots were needed by which 
plants could utilize these resources. As man, standing 
on the bank of the stream and looking for means to 
better his condition, was led to put his wheel into the 
water and withdraw some of the energy running by un- 
used, so have plants, during the long ages of fitting and 
refitting, learned to build into the capillary and percola- 
tion streams which flow past the grains of soil such 
wonderful systems of absorbing surfaces as we have 
seen that greatest of American food plants, the maize, 
to possess, and of which America's most revered poet 
wrote, in 1855 : — 

Day by day did Hiawatha 
Go to wait and watch beside it ; 
Kept the dark mold soft above it, 
Kept it clean from weeds and insects, 

* $ $ * # 

Till at length a small green feather 
From the earth shot slowly upward, 
Then another and another, 
And before the summer ended 
Stood the maize in all its beauty, 
With its shining robes above it, 
And its long soft yellow tresses ; 



212 The Soil. 

And in rapture Hiawatha 

Cried aloud, " It is Mondamin ! 

Yes, the friend of man, Mondamin ! " 

Then he called to old Nokomis 

And Iagoo, the great boaster, 

Showed them where the maize was growing, 

Told them of his wondrous vision, 

Of his wrestling and his triumph, 

Of this new gift to the nations, 

Which should be their food forever. 

And still later, when the Autumn 

Changed the long green leaves to yellow, 

And the soft and juicy kernels 

Grew like wampum hard and yellow, 

Then the ripened ears he gathered, 

Stripped the withered husks from off them, 

As he once had stripped the wrestler, 

Gave the first feast of Mondamin, 

And made known unto the people 

This new gift of the Great Spirit. 

Looking at Fig. 30, which shows the roots of winter 
wheat, barley, oats, blue grass,, timothy, clover, and 
another leguminous plant, Lathyrus sylvestris, it will 
be observed that with these plants, all except the blue 
grass send their roots into the fourth foot of soil, and 
in these cases, as with the corn, there is no portion of 
soil in the upper three or four feet which a root can 
penetrate that is not threaded by roots much closer to- 
gether than one in every cubic inch. Not all of the roots 
belonging to the tops shown in the figure just referred 
to were retained, but simply those which grew vertically 
downward within the area of a circle 12 inches in 
diameter. 

How great may be the mass of roots associated with 
the tops of clover, oats, and barley, is clearly shown in 



Need and Grreat Extent of Root Surface. 213 

Fig. 28, where the total root system of these plants was 
recovered from the soil in which they grew. It is very 
probable that, had the cylinders been deeper in which 
these plants were grown, their roots would have attained 
a greater length, and this would certainly have been the 




Fig. 30. — Showing the vertical distribution, under field conditions, of 
the roots of blue grass, timothy, Lathyrus sylvestris, clover, winter 
wheat, barley, and oats. 

case with the clover, whose roots matted thickly at the 
bottom of the barrel in which they grew. 

Looking at the roots of winter wheat in Fig. 30, it will 
be seen that a mass of other roots have been entangled 
with them at a depth of 2 to 3 feet below the surface. 
These are from a second-growth black oak standing in a 
pasture 33 feet distant from the place where the sample of 



214 



The Soil 



wheat roots were taken. In Fig. 31 may be seen the roots 
from a smaller tree of the same species as they were 
drawn from a sandy soil with the aid of a stump puller. 
In digging in a field adjacent to an apple orchard, the 
writer has found roots of the apple as large in diameter 
as a slender lead pencil at a distance of 45 feet from the 
trunk of the tree to which it was attached. 




Fig. 31. — Showing the roots of second-growth black oak as drawn 

from a sandy soil. 

Such facts as these illustrate in a forcible manner how 
deeply and broadly the roots of plants are sent foraging 
through the soil, and how much soil it is needful for 
them to come in contact with in order to procure the 
food and water they need. 

Schubart, a German farmer, Storer tells us, made 
measurements of various roots which he washed out 



Need and Great Extent of Root Surface. 215 

from the soil of fields where the crops were growing. 
He found the roots of wheat, sowed in September, ex- 
tending to a depth of 7 Rhenish feet in a subsoil com- 
posed of sandy loam ; and Lawes observed the roots 
of lucern penetrating to a depth of 9 feet below the 
surface. 

Referring again to the roots of maize which we re- 
covered from the field at different stages of maturity, it 
may be stated here, as having an important bearing on 
the depth of cultivation of this crop, that as the corn 
advances towards maturity a portion of the roots which 
are thrown off at higher levels on the stem develop more 
nearly horizontally and come closer and closer to the 
surface, making it more difficult to cultivate deep late in 
the season than when the corn is small. 

At the time when the corn had a height of about 18 
inches, July 9, the roots in the centre between the rows 
3.5 feet apart were nearly 8 inches below the surface, 
rising in a festoon to near the surface of the ground at 
the hill on either side. At this time, too, most of the 
roots were confined to the upper 18 inches of soil. 
When the corn had attained a height of 2.5 to 3 feet, 
the surface leaders, midway between the rows, had risen 
to within 6 inches of the top of the ground and now 
occupied the upper 2 feet of soil. Just as the corn 
was coming into tassel, the upper leaders were then 
scarcely 5 inches below, while at maturity they were 
less than 4 inches from the surface. 

It is evident from these facts that corn may safely be 
cultivated more deeply early in the season than when it 
is more mature. 

Each of the trunk roots or leaders of the corn plant 
sends out on opposite sides, much as the stalk does its 



216 The Soil 

leaves, slender rootlets from 2 to 6 inches long, and 
those on the surface leaders rise directly upward and 
nearly reach the top of the ground in the latter part of 
the season. 

Those soils which are sandy and loamy in character 
rather than clayey, and whose grains have little tendency 
to draw together into block-like masses of varying sizes, 
as do the stiff clays, allow a much more symmetrical de- 
velopment of the roots in them, and as a consequence of 
this there is less trespassing of one root upon another ; 
there is not so much soil far removed from the root hairs, 
and hence the soil water is more easily, rapidly, and 
completely removed for the purposes of the plant, and 
finally in these soils the roots find less difficulty in wedg- 
ing the soil grains apart as they need more room in their 
growth. 

In the clayey soils, too, as they shrink and crack, draw- 
ing themselves together in small cube-like blocks, there 
is a tendency, during dry seasons, to tear or break off 
many of the smaller rootlets, and thus deprive the plant 
of its means of water supply when water is most needed, 
and when, if the roots were left intact, it might be had. 

There seems to be operative in the plant a power or 
directive influence, which leads to the most rapid growth 
of roots in those directions in the soil where the most 
bountiful supplies of food and the best conditions for 
growth exist. 

When cultivated fields lie along one side of a grove or 
row of trees, these trees develop the strongest roots 
beneath the tilled fields, in just the same manner as the 
branches grow most rapidly in the direction of the most 
sunshine and the largest amount of room. Whether the 
lines of most rapid growth are determined solely by, and 



Need and Great Extent of Root Surface. 217 

are the result of the most complete feeding, — that is, 
whether those roots which lie where the most food mate- 
rials in the form of water and ash ingredients can diffuse 
into them, are in precisely the condition which causes the 
assimilated material from the stem to be brought to the 
roots to make a more rapid growth possible, — need not be 
discussed here. It is true, however, that a plant does 
not usually waste its energies in developing roots in a 
direction where no benefit could be derived from it. 



CHAPTER VIII. 

SOIL TEMPERATURE. 

There is no physiological fact more evident than the 
extreme importance of maintaining the right temperature 
surroundings for living forms of all kinds. In our own 
case a deviation of the mean temperature of the body 
a few degrees either above or below 98° F. results in 
very serious consequences, if long continued. So impera- 
tive is the right bodily temperature in many animals, 
and so narrow is the admissible limit of variation, that 
it is necessary to have in the body compensating devices 
which are automatically under the control of the nervous 
system. When we are in health if, for any reason, the 
mean temperature of the body is becoming too high, the 
sweat glands are set at work and the surface of the body 
covered with perspiration, the evaporation of which with- 
draws so much heat from the body that the temperature 
is brought down to the normal point. Then, should the 
temperature tend to fall too low, the activity of the skin 
is diminished, and at the same time a larger amount of 
oxygen is taken into the body to unite with the food eaten, 
for the definite object of producing heat more rapidly. 

In the vegetable world the extremes of temperature 
which are destructive to life are usually much farther 
apart than they are among animals ; that is, the tempera- 
ture may be allowed to fall much lower and to rise much 
higher with no other serious consequences than the 

218 



Soil Temperature. 219 

partial or complete cessation of physiological processes, 
but usually here there is both an upper and a lower limit, 
beyond which life is destroyed. 

It is not difficult to understand why these temperature 
relations should be so essential, and from the practical 
point of view it is very important that they should be. 
Many of the essential changes which take place in the 
body of a plant or of an animal, and which constitute the 
life processes, are chemical in their character, as is that 
of the burning of wood. But when we desire wood to 
burn, in ordinary air, when we wish oxygen to unite with 
it chemically, we have first to apply heat to it and raise 
its temperature up to a certain point before burning will 
begin. When the chemical action has been once started, 
then there is usually heat enough produced to maintain 
the action so long as there is a plentiful supply of oxygen 
and of wood. Then, when water is thrown upon a fire to 
extinguish it, it does so chiefly by withdrawing heat from 
the flames so rapidly in the evaporation of the water that 
the temperature is lowered to such an extent as to stop 
the chemical action. The steam formed by the evapora- 
tion also occupies so much space as to greatly dilute the 
oxygen, and in this way tends to make the burning slower 
or to stop it altogether. 

To light the match, we rub it vigorously upon some 
rough surface, but this is only to raise its temperature 
up to the point at which oxygen will begin to unite with 
it ; to warm the prepared end in any other way would 
produce the same result, and the sole reason for using the 
preparation at the end of the match is because chemical 
action can be started in it at a temperature so low that 
it can easily be produced by friction. 

Now the chemical changes in the animal body and in 



220 The Soil. 

the tissues of plants, which result in the various phe- 
nomena of growth and manifestations of power, require 
that the materials which react one upon another should 
first be raised to a certain temperature, should have a 
certain rate of molecular swing, before it is possible for 
the changes to take place. Just as water evaporates the 
faster the more heat is communicated to it whereby its 
molecules, by absorbing that heat, are thrown outside of 
the liquid mass and become a gas ; and just as the fuel 
in the stove must be warmed up to a certain temperature 
before the force of cohesion is enough weakened to allow 
the oxygen of the air to unite with it; so must the 
materials within the seed, m the roots, stems, and leaves 
of plants have their temperature raised to a certain point 
before those chemical and physical changes which con- 
stitute the phenomena of growth can take place. 

IMPORTANCE OF SOIL WARMTH. 

Now the lowest soil temperature, according to Eber- 
mayer, at which the processes of growth are started in 
most cultivated crops is from 45° to 48° F., but the maxi- 
mum results are attained only after the soil has reached 
a temperature of 68° to 70°. Let us compare these tem- 
peratures with those observed in the soil at different 
depths, for the six months, April to September inclusive. 
Dr. Frear reports the soil temperatures at State College, 
Pennsylvania, from which we derive the mean of five 
years, as given in the table below : — 



Depth. April. 


May. 


Jink. 


July. 


Aug. 


Sept. 


3 inches 43.74 


55.13 


67.20 


70.16 


68.70 


61.32 


G " 43.08 


54.72 


66.34 


60.75 


68.49 


61.70 


12 " 42.00 


53.83 


05.03 


08.80 


68.66 


62.73 


24 " 41.43 


51.45 


61.00 


66.42 


67.41 


63.59 



Importance of Soil Warmth. 221 

These temperatures, it will be observed, for the month 
of April, are below the minimum for growth given above, 
while the August temperatures only barely reach 68° F. 

Ebermayer, at Munich, found the temperatures in a 
loess-like loam as follows, for a mean of four years : — 

Depth. April. May. June. July. Aug. Sept. 



5.9 inches 


44.65 


56.79 


61.11 


67.26 


64.09 


58.21 


11.8 " 


44.31 


57.51 


60.06 


66.16 


63.61 


57.88 


23.7 " 


44.40 


53.58 


59.11 


63.12 


(53.0^ 


58.82 


35.4 " 


43.56 


51.24 


57.33 


62.92 


62.26 


58.51 



These temperatures, it will be observed, are higher in 
April and May, but lower the balance of the season, than 
they are in Pennsylvania. 

Now if it is true that the vital processes of plant life 
can only go forward rapidly and normally when the 
surrounding temperatures are right, it is evident that 
this factor in the culture of plants must be of even 
greater importance than it is in the successful manage- 
ment of animals; for the latter have it within their 
power to raise or lower their own bodily temperature 
as the surrounding conditions may demand, Avhile this 
power is not to any notable degree possessed by plants. 

Let us then consider some of the ways in which too 
low or too high soil temperatures may work to the dis- 
advantage of a crop growing upon it. It may be stated 
at the outset that in temperate climates, where the soils 
are supplied with the needed amount of moisture, there is 
little likelihood that the temperature will become too 
high for the majority of our cultivated crops. The dan- 
ger lies in the direction that the soil will be too cold. 

If we desire to dissolve almost any substance quickly 
in water, or indeed in almost any acid, we can greatly 



222 The Soil. 

hasten the solution by using heat; and from what has 
been said regarding the method of solution, this should 
be expected. But one of the chief functions of soil 
water is to take into solution, from the soil constituents, 
substances which, for the most part, dissolve, under the 
most favorable conditions, very slowly. Now, raising 
the temperature of the soil grains, weakens the attractive 
force which holds the plant food locked in the solid 
state, while at the same time it makes the diffusion of 
the dissolved materials, away from the seat of action, 
more rapid; and unless the dissolved materials are 
removed as soon as formed, they, by their reaction 
against the face of the soil grains, tend to prevent any 
further action from taking place. 

It is not only important that there should be a rapid 
diffusion of the dissolved food away from the places 
where it is being formed, through the action of soil 
water, but it is even more important that this process 
should be carried forward in the soil air, in order that 
a sufficient amount of fresh oxygen and nitrogen should 
enter the soil to replace that which is being used by 
roots, seeds, micro-organisms, and chemical processes 
needful to a fertile soil ; and the higher the soil tem- 
perature is, the greater are the absolute velocities of 
the molecules of air, and the faster will they reach the 
place in the soil where they are needed, and the sooner 
will the rapidly forming carbon dioxide escape into the 
air, leaving room for more to form. A high soil temper- 
ature, then, is conducive to a more rapid and thorough 
soil aeration or ventilation, a process of extreme impor- 
tance, as we shall see in another place. 

It is not enough that a rapid solution of plant food 
shall take place in the soil, but in order that growth 



Importance of Soil Warmth. 223 

may be vigorous, it is necessary that the dissolved food 
should be transported quickly to the places in the plant 
where it is to be used. Now the strength of osmotic 
pressure, and the rate of its action, increases as the tem- 
perature of the medium in which it is taking place is 
higher. We must keep in mind that in the process of 
osmosis, as in the diffusion of gases or in the evaporation 
of water, the molecules go from place to place by virtue 
of the rate at which they are thrown by the heat imparted 
to them, and hence, if the soil temperature is held high, 
the molecules of water are hurled into the root hairs and 
on into the other tissues faster than they can be if the 
surrounding temperature, the supply of power, is low ; 
but when the molecules are once within the plant cells, 
then the higher speed they possess in virtue of their 
higher temperature is just the condition which develops 
the strong osmotic pressure required to force the sap 
onward toward and into the leaves, no matter how high 
the stem which bears them may be. 

Sachs has shown, for example, in the case of both the 
tobacco plant and the pumpkin, that they wilted even 
at night and with an abundance of moisture in the soil, 
so soon as the soil temperature fell much below 55° F. 
Under this temperature the power which moved the 
water from the roots to the leaves was too feeble to 
compensate for the slow evaporation which takes place 
at night. 

Then, again, when seeds germinate in the soil, work 
must be done, and in no small degree, at the expense of 
the heat absorbed by the soil. Haberlandt found, for 
example, that the germination of wheat, rye, oats, and 
•flax goes forward most rapidly at 77° to 87.8° F., and that 
corn and pumpkins germinate best at 92° to 101° F. "He 



224 The Soil. 

found that when corn would germinate in three days at 
a temperature of 65.3° F., it required eleven days when 
the temperature of the soil was as low as 51° F. He 
found, further, that when oats would germinate in two 
days impelled by a temperature of 65.3° F., it required 
seven days to do the same work when the temperature 
was as low as 41° F. 

These are forcible illustrations of the need of a warm 
soil, and should be a sufficient spur to every thoughtful 
farmer to do whatever he can to meet the conditions 
here made evident. That certain seeds require a higher 
soil temperature for their germination than others do, 
must be understood as meaning that the necessary trans- 
formations do not take place so easily. It must not be 
understood, however, that when a seed is placed in a 
cold soil, the food stored in it for the development of the 
young plant cannot undergo a change. Quite the con- 
trary ; there are organisms in the soil which are able to 
do their work at low temperatures, and if a seed, under 
these conditions, comes into their presence, it absorbs 
moisture and, being unable to grow, becomes a prey to 
these lower forms and decays. 

In speaking of the sources of nitrogen for higher 
plants, it was stated that the nitrates formed their chief 
supply. But in studying the conditions under which the 
nitric ferment works most vigorously, it has been learned 
that the germs cease to develop nitric acid from humus 
when the temperature falls below 41° F. ; that its action 
is only appreciable at 54° F., while it becomes most vigor- 
ous at 98° F., but that at 113° F. its activity drops back 
again to what it was at 59° F. Here, again, is another 
and very urgent need for the right soil temperature. 

What, then, are the conditions which influence soil 



Conditions Influencing Soil Warmth. 225 

temperatures ? And, since a soil is more often too cold 
than too warm, what can be done to raise its tem- 
perature ? 



CONDITIONS INFLUENCING SOIL WARMTH. 

There is no one cause so effective in holding the 
temperature of a soil down as the water which it contains, 
and which may be evaporating from its surface. This is 
because more work must be done to raise the temperature 
of one pound of water through one degree than of almost 
any other substance. Thus, while 100 units of heat must 
be used to raise 100 pounds of water from 32° to 33° F., 
only 19.09 units, according to R. Ulrich, are required to 
warm the same weight of dry sand, and 22.43 units an 
equal weight of pure clay, through the same range of 
temperature. To raise the temperature of 100 pounds 
of dry humus through 1° F., it is necessary to give to it 
44.31 heat units, while 100 pounds of carbonate of lime 
require 20.82 units. 

From these figures it is evident that when the sun 
imparts equivalent amounts of heat to equal weights of 
sand, clay, humus, and water, the sand will be the warm- 
est, while the water will be the coldest. To make the 
differences definite, suppose the water has its tempera- 
ture raised 10° F., then the same amount of heat enter- 
ing an equal weight of humus will make it 22.6° warmer, 
clay 44.58° and sand 52.38° warmer. But while the tem- 
peratures of these soils would stand in the relation of the 
figures here given when they are dry, it is not true that 
under field conditions such large differences of tempera- 
ture would be observed, because there are other factors 

Q 



226 The Soil. 

which modify the effect of differences of specific heat, 
whose influence alone we have thus far considered. 

Since the weights of dry soils per cubic foot are not 
the same, it is evident that the heaviest soil, were other 
conditions alike, would be the coolest, because while the 
same amount of sunshine can fall upon a square foot of 
sandy soil as falls upon an equal area of clay soil, the 
cubic foot of sand weighs 110 pounds, while that of 
clay may only weigh 75 pounds ; hence, a surface foot of 
sandy soil, instead of being 7.8° warmer, would be 8.6° 
colder than the clay soil. But the fact that the water- 
holding power of the clay soil is greater than that of the 
sandy soil, works again in the opposite direction, on ac- 
count of the large amount of heat needed to warm the 
water, to make the clay colder than the sand ; so that, if 
we assume the clay and sand saturated, the same number 
of heat units per surface foot of each soil would give the 
sand a temperature 3° F. warmer than the clay. 

The chief cause, however, which makes a wet or un- 
drained clay soil colder than a well-drained or sandy soil is 
the large amount of heat which is used up in evapora- 
ting the excess of water from the surface. While 100 
heat units will raise the temperature of one pound of 
water through 100° F., it is necessary to use 9G6.6 heat 
units to evaporate one pound of water from the soil ; 
but this, if withdrawn directly from the cubic foot of 
saturated clay, would lower its temperature about 10. 3° F. 
It must be evident therefore, that to allow the surplus 
water to drain away from a field rapidly, rather than to 
hold it there until it has time to evaporate, must greatly 
favor the warming of the soil. 

The writer has observed the following differences of 
temperature in the surface inch of a well-drained sandy 



Conditions Influencing Soil Warmth. 227 

loam and an imdrainecl black marsh soil, both of them 
naked and level. 



Date. 


Time. 


Condition of 
Weather. 


a 

o 

a 
« 
u 

< 

a 
a . 

& M 
a<J 


a 
o 

a 

a © 

h q 
< a 
a z 
a 2 

S| 


o 

& a 


a' 
o 

a 

a 

a 
a 

a 

n 


Apr. 24 


3.30 to 
4.00 p.m. 


Cloudy, with 
brisk east 
wind. 


60.5° F. 


66.5° 


54.00° 


12.50° 


Apr. 25 


3.00 to 
3.30 p.m. 


Cloudy, with 
brisk east 
wind. 


64.0° F. 


70.0° 


58.00° 


12.00° 


Apr. 26 


1.30 to 
2.00 p.m. 


Cloudy, rain 
all the fore- 
noon. 


45.0° F. 


50.0° 


44.00° 


6.00° 


Apr. 27 


1.30 to 
2.00 p.m. 


Cloudy and 
sunshine, 
wind S.W. 
brisk. 


53.0° F. 


55.0° 


50.75° 


4.25° 


Apr. 28 


7.00 to 
8.30 a.m. 


Cloudy and 
sunshine, 
wind N.W. 
brisk. 


45.0° F. 


47.0° 


44.50° 


2-.50° 



It should be noted in connection with this table that 
the differences in temperature in favor of the drier soil 
have occurred when the amounts of evaporation would be 
relatively small, and hence when the differences would be 
below rather than above the average. 

Comparing the temperatures of a well-drained clay soil 
with that of a sandy loam, also well drained, when each 



1st Foot. 


2d Foot. 


3d Foot. 


76.5 C F. 


74.7° F. 


72.1° F. 


69.5° 


60.3° 


67.0° 



228 The Soil. 

was less than half saturated, the following differences 
were observed on August 6 : — 

Sandy loam . . . 
Clay loam . . 

Difference, 7.0° 5.4 C 5.1° 

Now, from what has been said in regard to the advan- 
tages of a warm soil, it is plain why a sandy loam, when 
well fertilized, is for so many purposes superior to the 
heavy clay soils. 

The slope of the land surface, and the direction of this 
slope with reference to the points of the compass, often 
have a marked effect upon the temperature even when 
the soils are identical. Thus, on the south shore of Lake 
Superior the writer found the temperature of a stiff red 
clay on a level table and on a south exposure sloping 
about 18° to have the following values on July 31 : — 

1st Foot. 
Bed clay, south slope 70.3° F. 
" " level 67.2° 

Difference. 3.1° 2.7° 2.8 C 

In a level, sandy, alluvial soil close by the above and at 
the same time, the temperatures were 71.2° F. 70.1°, and 
67.6° for the first, second, and third feet respectively. 
Here, again, the influence of the character of the soil on 
its temperature is well marked, but the differences are 
smaller than in the former case, as the tabulation shows. 
In these two cases both soils were more than half saturated 
with water : — 



2d Foot. 


3d Foot. 


68.1° F. 


66.4° F 


65.4° 


63.6° 





1st Foot. 


2d Fo..r. 


3d Foot. 


Alluvial sand, level 


71.2°F. 


70. 1 F. 


07.6° F. 


Red clay, level 


07.2° 


65.4 


63/ 



4.0° 4.7 4.1> 



Conditions Influencing Soil Warmth. 229 

Wollny, in his study of soil temperatures as affected 
by slope and direction of exposure to the sky, found, 
through observations on small artificial hills with incli- 
nations of 15° and 30° to the horizon, that the south side 
has an average temperature of 1.5° F. when the slope 
was 15°, and 3.1° F. with a slope of 30°, warmer than the 
north side ; but, comparing the east with the west slope, 
he found less than .2° F. difference. Comparing the east 
and west slopes with the south, he found, for 15° inclina- 




Fig. 32. — Showing how the slope of the surface influences the amount 
of heat received per unit area. 



tion, the east .71° F. and the west .56° F. colder than the 
south side ; but when the 30° slopes were compared, 
the differences were 1.31° F. for the east and 1.44° F. for 
the west colder than the south slope. 

Just why a south slope should be warmer than a north 
slope will be readily seen from an inspection of Fig. 32. 
Suppose A65B represents a prism of sunshine falling 
upon the hill AEB, where AE is the south slope and EB 
the north. Here it will be seen that, on account of the 



230 The Soil 

sun not being directly above the hill, the south slope gets 
as much more sunshine than the north slope does as the 
line 46 is longer than the line 45 which, for the angle of 
20°, is about one-third more per each square foot of sur- 
face. 

The color of a soil, too, has not a little influence in de- 
termining its temperature, the darker soils, if other condi- 
tions are the same, being the warmer. All are familiar 
with the fact that a black garment is much warmer in 
bright sunshine than a white one. This is because the 
black surface absorbs the ether waves as they come from 
the sun in much larger proportions than the white gar- 
ments do. The leaves which drift upon the white snow, 
and the dirt also, as all have observed, cause the snow to 
melt much more rapidly than where the snow is clean 
and white. So the sandy soils which are light in color 
do not become as warm as they might if their light 
color and glistening surface did not cause much of the 
sunlight to be turned directly back without doing any 
work upon them. 

A rough, uneven, lumpy, or ridged surface has a ten- 
dency to make the soil colder than the smoother, more 
nearly level surfaces do, and there are several causes 
which co-operate to produce these results. If the surface 
is ridged east and west, or if it is covered with lumps, the 
south sides of these inequalities receive more heat than 
the north sides do, causing them to become relatively 
very warm, and in this condition they lose much more 
heat by radiating it away and by the air coming in 
contact with and being warmed by them. 

The effect of rolling the land on the temperature of the 
soil is often very marked, its general tendency being to make 
it warmer during bright clear weather, but in cloudy and 



Conditio7is Influencing Soil Warmth. 231 

cold weather it has the opposite effect, rolled land tend- 
ing to cool more rapidly. The writer has found through 
extended studies, under field conditions on soils of vari- 
ous kinds, that a rolled field may have a temperature, at 
1.5 inches below the surface, as much as 10° F. above en- 
tirely similar soil not so treated, and at a depth of 3 
inches, a difference of 6.5° has been observed. The dif- 
ferences in temperature observed on one date are shown 
in Fig. 33. Here, it will be seen, the air temperature 




Fig. 33. — Showing observed differences of temperature on rolled and 
on unrolled ground. 



over the unrolled ground is warmer, except early in the 
morning, than it is over the rolled surface, showing that 
the dry lumps and uneven surface are imparting their 
heat to the air more rapidly, and, since both surfaces are 
receiving the same amounts of heat from the sun, it is 
plain that if the air is warmed more over the unrolled 
ground the soil must be warmed less. The fact that the 
surface soil is less firmly packed on the unrolled ground 
also causes the heat to be conducted downward less rap- 
idly, and thus tends to make the deeper soil cooler. Dux- 



232 



The Soil. 



ing the night and cold, cloudy weather, when little heat is 
being received from the sun, the loose soil on the unrolled 
land acts as a blanket and tends at such times to make 
the rolled land the coolest at the surface, as shown in the 
figure. 

The observed temperatures between 1 p.m. and 4 p.m., 
on eight Wisconsin farms, are given below : — 











< 

W 

s 

w 
H 

■3 


Soil Temperatures. 


Soil. 


At 1.5 Inches. 


At 3 Inches. 




Kolled. 


Unrolled. 


Rolled. 


Unrolled. 




F. 


F. 


F. 


F. 


F. 


Sandy 


56.75° 


65.55° 


63.50° 


61.92° 


59.45° 


Clay loam 








51.17° 


56.55° 


53.60° 


56.48° 


53.55° 


a c; 








59.00° 


70.21° 


64.40° 


64.85° 


59.90° 


Sandy . . 








69.62° 


73.40° 


72.05° 


70.79° 


69.26° 


Clay . . 








72.64° 


79.77° 


78.20° 


73.02° 


71.82° 


Sandy clay 








73.30° 


76.83° 


71.90° 


72.58° 


69.09° 


Yellow clay 








60.80° 


61.34° 


58.82° 


57.38° 


55.58° 


Clay loam 








79.70° 


89.89° 


86.12° 


81.49° 


76.47° 


Mean . 


65.37 


71.69 


68.57 


67.31 


64.39 


Difference 




3.12 


2.92 


. . . 



These results were all obtained in the spring, on land 
sowed to grain, and show an average difference of 3.1° F. 
and 2.9° F. higher temperature on the rolled ground. 

The character and depth of cultivation also has an 
appreciable effect upon the soil temperature, stirring it 
deeply, tending to make the deeper soil cooler than where 
the depth of cultivation is less. This tendency is due to 
the fact that the loose soil of greater depth is a poorer 



Conditions Influencing Soil Warmth. 233 

conductor of heat, and tends to shut out the heat from the 
sun. The temperatures where corn ground was cultivated 
3 inches deep and 1.5 inches deep were found by the 
writer to be .82° F. warmer in the surface foot, .59° F. in 
the second foot and .36° warmer in the third foot on land 
cultivated 1.5 inches deep than they were on adjacent and 
similar soils cultivated to a depth of 3 inches. These 
differences were determined by a self-recording maxi- 
•mum and minimum thermometer, which had a bulb one 
foot long, enabling it to record the mean temperature of 
the foot of soil in which it was placed, and the differ- 
ences given above are the means of measurements in 
eleven fields in different parts of Wisconsin. 

It is also true that the fermentations of organic matter 
which go on in the soil under the influence of various 
microscopic organisms, produce no inconsiderable amount 
of heat, and for this reason, among others, a field heavily 
fertilized with farmyard or green manures enjoys a higher 
soil temperature because of the treatment. 

There is perhaps no method of soil warming at consid- 
erable depths in the ground so effective as that of warm, 
percolating rains. In the spring of the year the soil is 
usually thoroughly saturated with the water from the 
winter rains and melting snows, and under these condi- 
tions, when the warm spring rains come they usually 
percolate deeply into the ground, shoving the colder soil 
water in front of them beyond the depth of the root zone. 
When we recall that each pound of rain at 60° F. carries 
10 heat units into the ground, which can be applied to 
raising the temperature of soil colder than 50° F. up to 
that point, and that each such heat unit can raise 
the temperature of a pound of sand 5.24°, the great 
advantage of warm April showers in bringing an early 



234 The Soil 

spring can be appreciated. But of course, when cold 
rains come to the fields, the opposite effect must result. 

It is evident therefore, from what has been said regard- 
ing the temperature of soils, that not only is the right 
degree of warmth very important, but the farmer has it 
within his power at times to make the soil warmer or 
colder. It will be remembered that the vital processes 
of plant life only begin after the temperature has risen 
above 45° to 48° F., while the mean April temperatures of 
soils cited on a preceding page fall below these figures, 
and since the earlier we can bring the soil up to the 
growing temperature the larger will be the conservation 
of both soil moisture and other plant food, it is evident 
that if we can, without undue expense, hasten the warm- 
ing of the soil to a practical extent, it is important that it 
should be done. 



MEANS OF CONTROLLING SOIL WARMTH. 

Now the thorough preparation of the seed bed which 
good farmers so much insist upon is justified in a large 
measure by the warming effect which judicious, thorough 
tillage has. In the first place, the development of a mulch 
over the ground lessens the loss of water from, the surface 
by evaporation, and if by this means we have saved from 
loss into the air 10 pounds of water per square foot, we 
have avoided by this saving the withdrawal of 10 times 
966.6 heat units from the same area; so that early thor- 
ough tillage not only saves moisture, but it at the same 
time permits the seed bed to become quickly both dry 
and warm enough to allow nitrification to begin and to 
hurry forward. It is very important, too, that this should 



Means of Controlling Soil Warmth. 235 

be clone ; for the melting snows and spring rains have car- 
ried down beyond the reach of young plants most of the 
soluble nitrates the soil may have possessed the fall be- 
fore. Early thorough tillage, then, develops to an impor- 
tant extent needed plant food by warming and aerating 
the soil, while at the same time it hastens the germina- 
tion and gets the plant into condition to take advantage 
of the food being prepared. 

It is not so important early in the spring that the ground 
should be warmed deeply, but better only so far as to 
provide ample available plant food for the start, and 
room enough for the first roots, and this is what early 
tillage does; the loose, open soil conducts neither the 
cold ground water up to become still colder by evapora- 
tion, nor the absorbed sunshine down where it is not yet 
needed. In effect this method converts the whole field 
into a hotbed or cold frame, and commences irrigation 
by saving water at the start. It does even more ; for 
while it develops early a little soluble plant food, it 
holds in abeyance these processes in the deeper soil, 
which, by starting too early, would cause a needless loss 
by developing nitrates which may be leached away 
before the crop has its roots ready to use them. 

We have pointed out how and to what extent rolling 
warms the soil. Should the farmer use his roller to 
warm his soil? Yes, at times; but he must do so with 
good judgment. From what has been said, it follows 
that rolling may warm the ground too deeply, and at the 
same time waste soil moisture. Evidently the practice 
to follow, so far as the problem here under consideration 
is concerned, is to wait after using the tool only so long 
as to permit enough moisture to reach the surface, and 
enough warmth to pass downward to meet the imme- 



236 The Soil 

diate needs, and then the harrow should follow without 
a moment's delay. 

A roller, to do its work properly, must have a con- 
siderable weight, and the larger the diameter of the 
roller, the heavier it should be. The plank can seldom 
be used as a substitute for the roller, when firming the 
ground is what is demanded. This will be readily 
understood, when it is recalled that the much lighter 
weight the plank must have is spread out over many 
times the extent of surface covered by the roller, and 
hence its pressure, per square foot, must be proportion- 
ately less. The roller presses, with its whole weight 
concentrated, along a narrow line, and the narrower the 
smaller the diameter of the roller. But the smaller the 
diameter of the roller, the harder it must draw in pro- 
portion to its weight. 

When a mellow, open seed bed has been prepared, and 
its temperature has been raised to the proper point, 
should a rain fall upon it, that water will tend to pass 
through its wide pores quickly to the deeper soil, and 
without leaching it as badly as would be the case were 
the soil more compact; so that in the early season when 
there is an over-abundance of moisture, it is best, for 
warmth, for aeration, and to lessen loss of fertility by 
percolation, to have a mellow seed bed. 

It seems to the writer probable that there may be 
times when we should till the surface for the express 
purpose of keeping the deeper soil cool even late in the 
season, when it has become desirable that it should have 
a good degree of warmth. Reference has already been 
made to the diurnal changes in the ground water, due to 
diurnal oscillations of soil temperature. But under cer- 
tain conditions these oscillations result in a loss of 



Means of Controlling Soil Warmth. 



237 



soil moisture through increased drainage, and with this 
an increased loss of plant food. 

In Fig. 34 are shown automatic records of the diurnal 
changes in the level of the ground water in a tile-drained 
field, and of the rate of flow of water from the system 
of tiles which was carrying the percolating waters 
away. The highest portions of these curves mark the 



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/ / ~\ 


"lL 


Zj cT "• 


_J g^-v ^7* 


7 > v t^-^-^^9^ i.r 


+Y\* 


U ■ ■ 


)t _ - 



Fig. 34. — Showing the diurnal oscillations of the water table and of 
the rate of flow of water from a tile drain due to diurnal tempera- 
ture changes. 



time when the water was flowing slowest, and when 
the water in the wells stood at the lowest level, while 
the lower parts of the curves mark the time when the 
water was flowing fastest from the tile drains, when 
percolation was most rapid. Referring now to Fig, 35, 
which shows the changes in soil temperature 18 inches 
below the surface, and of the air temperature above, it 
will be seen that the warmest time in the soil is a little 



238 



The Soil. 



after midnight, while it is coldest a little after noon. 
The most rapid flow of water from the drain, and the 
highest level of the water in the wells, occur about 7 
o'clock in the morning, hence some hours later than the 
highest soil temperature ; and since it is the expansion 
of the soil air, due to the rising temperature, which pro- 
duces this effect, a certain amount of lagging should be 
expected. 




Fig. 35. — Showing diurnal changes in the soil temperature at 18 inches 
below the surface and of air temperatures one foot above the sur- 
face, as given by thermograph. 



Now in such localities as these, and possibly also 
where the ground water is not as near the surface, 
the developing over the field of a loose, non-conducting 
mulch of soil, produced by cultivation, must make the 
diurnal changes of temperature less, and hence the per- 
colation of the soil water also, saving the water for the 
crop. 



CHAPTER IX. 

THE RELATION OF AIR TO SOIL. 

The presence of an ample amount of air in the soil is 
as indispensable to the life of upland plants as is that 
of water, and whatever method of tillage is adopted, it 
should not hinder soil breathing to an injurious extent. 

It has been abundantly demonstrated that when free 
oxygen is completely excluded from seeds placed under 
otherwise good conditions for germination, growth will 
not take place ; if after seeds have commenced to sprout 
the oxygen supply is cut off, they cease to develop. It 
is true that the germination of seeds will take place in 
an atmosphere very poor in oxygen, but after the percen- 
tage amount has been reduced below -^ of the normal 
quantity, growth is much retarded and sickly plants 
usually are the result. 

NEEDS OF SOIL VENTILATION. 

Practical experience teaches that when a soil bearing 
other than swamp vegetation is flooded, or even if it is 
kept long with its pores filled with water, the plants 
soon sicken and die, and this, too, when they are in full 
leaf and abundantly supplied with food and warmth. 
The difficulty is the lack of root breathing; the plants 
are drowned, and as effectually as an animal would be 

239 " 



240 • The Soil. 

under water, because enough free oxygen cannot reach 
them. 

It is true, to be sure, that on the floating gardens of 
the Chinese and the Mexicans, crops are matured under 
conditions where the roots of the plants must be im- 
mersed in water during their whole period of growth, 
and this fact appears to be a contradiction of the state- 
ments just made. In these cases, great rafts of basket- 
work are covered with soil, and floated upon a lake or 
stream, so that here the roots of whatever crop the 
floating islands may have produced must have occupied 
saturated soil or the water itself below the raft. So, too, 
in the cases of water culture, where plants have been 
grown without soil, in water holding in solution the 
needed nitrogen and ash ingredients, there is an appar- 
ent contradiction. In these cases, however, the water 
is free from the soil, where, by absorption and diffusion, 
oxygen from the air can enter it even more readily 
than it is able to do in a good soil, for there a 
large part of the space is occupied by impenetrable soil 
grains; and more than this, wind and convection cur- 
rents are powerful adjuncts in bringing fresh oxygen 
to the submerged roots of the plants just as they are 
in bringing to the fish and other animals the oxygen 
they need. 

In the compact, water-filled soil, however, all current 
motion is prohibited, and the roots of plants can only 
secure the free oxygen which the water may have brought 
with it when it fell as rain, but as this amount is small, 
it soon becomes exhausted. On the other hand, if the 
field is underlaid by a deep, porous subsoil, into which 
the rains may quickly penetrate, or if the field is under- 
drained, then, as the water runs away, leaving empty 



Needs of Soil Ventilation. 241 

spaces behind, air must be drawn in to take the place, 
and needed oxygen is thus supplied. 

We have seen in another place, that the germs which 
develop nitric acid in the soil find oxygen indispensable 
to their life, and so important is a large supply of it in 
the soil that in olden times, when saltpetre farming 
was practiced to procure potassium nitrate for use in the 
manufacture of gunpowder, great pains were taken to 
thoroughly aerate the soil in which the nitrate was being 
developed, and as one of the chief objects of tillage is 
the production of nitrates in the soil, we may profitably 
recall the old method of raising saltpetre. 

In the growing of nitrate of potash in Europe, a mix- 
ture of soil, manure, and leached ashes or marl was 
formed into beds, sometimes made more open and porous 
by the use of gratings or racks. Great care was taken 
to keep the beds warm and of the proper degree of moist- 
ure, while from time to time they were shoveled over or 
otherwise stirred for the purpose of introducing air and 
warmth. Then when a new field or bed was to be 
started, care was taken to bring to it soil from an old nitre 
bed, or, in the language of that time, adding " mother of 
petre," a term so appropriate in the light of our knowl- 
edge of to-day that nothing more significant could have 
been used. It is thus seen that the old nitre farming 
found its best results, its largest yields of saltpetre, in a 
rich soil kept well moistened, well stirred, and thoroughly 
warmed, all of them conditions which we now recognize 
as very important for any crop, and we cannot doubt that 
they are so because they favor the rapid development of 
that important plant food, nitric acid. 

We have just been speaking of the need of oxygen in 
the soil to carry forward the process of nitrification. 

R 



242 The Soil 

It must now be said that oxygen is also needed to pre- 
vent the destruction of the nitrates after they have once 
been formed. From AVarington's review of our acquain- 
tance with the phenomena of denitriiication, we learn 
that the destruction of nitrates with the setting free of 
nitrogen in waters containing sewage was observed by 
Dr. Angus Smith in 1867, and in 1808 Schlosing showed 
that nitrogen gas, or some of its lower oxides, are set 
free in several putrefactive and fermentive processes. 
He also found that when a moist soil, rich in humus, 
was kept in an atmosphere of free nitrogen, from which 
all oxygen had been excluded, all nitrates which they 
may have contained quickly disappeared. He found, 
further, that the same denitrifying process took place 
when a limited quantity of ordinary air was present. 
It was even true with the soils rich in organic matter 
that they often gave off more free nitrogen than was 
represented by the nitrates present in them; that is, 
other organic nitrogen was broken down and set free, 
this process consuming the oxygen derived from the 
decomposed nitric acid. 

With these facts before us, it is plain that we are in 
danger of having the soil depleted of its needful Jiii rates, 
not only by excessive leaching, but also through the 
destruction of the organic matter from which these are 
evolved, if the land is allowed to remain too long with 
Insufficient ventilation, as the result of poor drainage. 

Warington conducted experiments in the Bothamsted 
laboratory on an artificially water-logged soil to which 
he had applied sodium nitrate at the rate of 519 pounds 
I mm- acre, and found that, in less than three weeks, all 
but 21 per cent of the nitrate had disappeared, its oxy- 
gen having been used in the carrying on of life prOQ- 



Needs of Soil I r entilation. 24o 

esses for which free oxygen would have been used had 
it been present in the soil in sufficient quantity. We 
must see to it, then, that our soils arc sufficiently venti- 
lated to insure the production of nitrates on the one 
hand, and to prevent their destruction on the other. 

Now that we "know how free nitrogen from the air is 
fixed in the tubercles on the roots of leguminous plants, 
it is evident that here is another reason why air must be 
admitted to the soil, and not simply to the sin lace layers 
which are tilled^ but deeply into the root zone two and 
three or more feet. It will be seen that oxygen must be 
admitted to the soil in order that the nitrogen of decay- 
ing organic matter may be converted into forms available 
to higher plants, while free atmospheric nitrogen is 
demanded to hold up the stock of organic nitrogen by 
making good the losses in the drainage waters and by 
the processes of denitrincation. 

Those fermenting processes which result in the return 
of carbon as carbon dioxide to the air after it lias 
answered the purposes of living tissues, require, many of 
them, oxygen from the air; hence, in order that the vast 
root systems which grow and die in the soil may not 
accumulate unduly, air in sufficient quantity must pene- 
trate deeply. We have sufficient evidence of the advan- 
tage of good ventilation in the strong heating of the 
well-aerated heaps of horse manure, when contrasted 
with the much slower fermentation which takes place in 
close cow dung, free from litter. 

There are many purely chemical reactions essential to 
soil production and soil fertility which demand a cer- 
tain measure of oxygen and carbon dioxide for their con- 
tinuance, so that here is another need for a fair measure 
of openness in the soil. And then if oxygen must be 



244 The Soil 

admitted to the soil for the setting free of nitrogen and 
carbon dioxide, it is equally necessary that these gases 
shall be allowed to escape with sufficient freedom, so 
that they shall not exclude the atmospheric air, or so 
dilute it as to render it ineffective. 

We have now in mind the chief needs for a sufficiently 
free passage of atmospheric air in and out of the soil. 
How, then, is soil ventilation accomplished? How is it 
hindered, and what may we do to control it? 



NATURAL PROCESSES OF SOIL VENTILATION. 

The most general and constant mode of interchange of 
gases in the soil, and in the air above, is that of diffu- 
sion, whose motive power is the sunshine absorbed by 
the surface layers. As the molecular motion of the soil 
grains increases during the day, as the temperature rises, 
a part is transmitted to the gases contained in its pores, 
and more of these molecules are driven out than enter it; 
but when the soil temperature falls, then the reverse 
condition takes place, so that we have in the upper layers 
of the soil an incessant temperature breathing. But if 
the surface of the soil did not warm and cool by turns, 
there would still be an interchange of soil and atmos- 
pheric gases so long as their compositions were not iden- 
tical; for, owing to the never-ending to-and-fro motion of 
the air molecules, wherever the oxygen is being con- 
sumed in the soil, there is produced at that place an 
oxygen vacuum into which other molecules are sure to 
find their way, unless the soil pores are in some way 
blocked to them. On the other hand, if carbon dioxide 
is being produced in the soil at any place, then an excess 



Natural Processes of Soil Ventilation. 245 

of pressure of this gas results, which pushes some of the 
molecules out into the open air. 

We have already seen how the temperature effect in the 
soil is felt even in the deeper ground water and to such 
an extent as to force it out into drainage channels. So, 
too, if for any reason carbon dioxide is more rapidly 
set free than it can escape, the increased pressure which 
results will affect the ground water in the same manner 
as the temperature changes do. In like manner a more 
rapid consumption of oxygen or nitrogen in the soil than 
is compensated for by inflow from above tends to develop 
a negative pressure on the soil water, which would per- 
mit capillarity to return to the soil spaces water which 
had been forced into the beginnings of drainage channels 
or passages. 

The aeration of the deeper soil is favored by the fact 
that, owing to the lagging of the diurnal changes of 
temperature to which reference has been made, the 
second foot may be growing warmer at the same time 
the surface foot is becoming colder, and vice versa. The 
second foot, for example, being warmest at the same time 
the surface foot is approaching its lowest temperature, 
more air from the second foot is forced into the surface 
foot by diffusion than would occur were there no tempera- 
ture lagging. Then in the daytime, when the surface 
foot is becoming warmest, while at the same time the 
second foot is growing colder, the air then diffuses more 
rapidly downward into the deeper soil. 

Every change which takes place in the barometer or in 
the atmospheric pressure above a field has a tendency to 
cause some air to pass either into or out from the soil. 
These alterations of pressure, in the soil air are so marked 
that the movement of the ground water is very sensibly 



246 



The Soil. 



affected by them, as will be seen by referring to Fig. 36, 
which shows the changes in the rate of flow of water 
from a spring as they were modified by variations in the 
atmospheric pressure. In Fig. 37, too, may be seen the 
changes of level of water in a well during 24 hours, most 
of which were coincident with fluctuations in atmospheric 



~E 



626 



i 



6 i2 6 



MA. 



3 



-j 



£££ 



4 



10 



12 




W-/ 



13 



S'26 



14 



6J2£ 



.1 

2 
3 

A 
^ 3 

6 
J 
B 
.9 



Fig. 36. — Showing fluctuations in the rate of flow of water from a 
spring at Whitewater, Wisconsin, May 4 to May 16, and the baro- 
graph record at Madison, Wisconsin, for the same period. Both 
reduced to natural scale. Heavy curve represents the spring. 



pressure. But every change in atmospheric pressure 
which is large enough to affect the level of water in 
wells must also be large enough to cause some air to 
enter or leave the surface layers of soil. 

When the wind is blowing strongly across the surface 
of the ground, but with greatly varying velocities, as is 
usually the case, there is a tendency to alternately suck 



Natural Processes of Soil Ventilation. 247 

air out from the soil pores, and again to allow it to 
return, thus producing an irregular but sometimes very 
strong soil breathing. This action of the wind is made very 
evident, too, oftentimes by the rise and fall of a carpet on 
the floor, and by the buckling of a tin roof as stronger 
and feebler gusts of wind pass in turn over the house. 

In certain sections of the country which are underlaid 
by extensive beds of coarse gravel, the wells sunk into 
these beds are often subject to strong draughts, which 
alternately pass into and out of them. In Sauk County, 
Wisconsin, there is a district of this sort where the air 




Fig. 37. — Showing the oscillations of water in a well during 2± hours, 
most of which were coincident with corresponding changes in the 
barometer. 



passes into the wells at times of high barometric pressure 
and in such large volumes in cold winter weather as to 
freeze and burst the suction and discharge pipes of pumps 
at depths greater than 70 feet ; then when a low pressure 
passes over the well, the outgoing current is so strong 
that even a hat may be lifted by it, and in winter the 
snow about the well is melted away. 

There are many prairies in various parts of the world 
which are underlaid with layers of coarse gravel, be- 
ginning at three to ten feet below the surface and often 
extending to depths of many feet. The soils of such 



248 The Soil. 

districts must be subject to a peculiarly strong venti- 
lation or breathing, which may have not a little to do 
with the wonderful productiveness usually characteristic 
of such lands. It will be evident, too, from what has 
been said, that sandy and otherwise light and open soils, 
especially when they are deep and the distance to the 
water table is large, will be subject to peculiarly thorough 
ventilation or breathing, while all close-textured soils, 
like the heavy and stiff clays, will naturally be aerated 
less perfectly. 



WAYS, OF INFLUENCING SOIL VENTILATION. 

This leads us to consider some of the means which are 
available to control soil breathing. It may be said at 
first that all methods of tillage which tend to develop 
large, open, non-capillary spaces in the soil must greatly 
facilitate the change of air, not only in that layer 
of soil so loosened, but at the same time in that which 
comes in contact with it below ; and in the more thor- 
ough soil breathing which deep tillage and the plow- 
ing in of coarse manure insures to the stiff clay soils, we 
find a large part of the good results which follow these 
treatments. 

Then when heavy lands are nnderdrained, these soils 
are so much better and more deeply aerated that we must 
look to this more complete ventilation for the chief ad- 
vantage which this type of land improvement assures. 
The aeration of the soil which is rendered possible by 
thorough underdraining has rarely been sufficiently em- 
phasized, neither has the method by which it is brought 
about been fully stated. 



Ways of Influencing Soil Ventilation. 249 

When the level of the ground water is permanently 
lowered 2 or 3 feet, as is done in underdraining, the 
roots of plants penetrate more deeply into the field, and, 
as they die and decay, leave a system of passage-ways 
leading toward the surface, into and out of which the 
soil air finds a more ready ingress and egress. Earth- 
worms, ants, and other burrowing animals also penetrate 
the ground more deeply, and thus form open ventilating 
flues of much larger magnitude than those left by the 
roots of plants. 

Then, again, as the under clays dry out, they shrink 
upon themselves and develop unnumbered fissures, through 
which the air more freely moves with every change of 
pressure and temperature, and in which the roots of 
plants place themselves, the better to profit by renovated 
air. With the deeper and more thorough penetration of 
the soil air, carrying with it the carbonic acid developed 
near the surface, it acts through the soil water upon the 
lime, producing the bicarbonate, which in its turn tends 
to flocculate the finer silt particles of the clay, causing 
them to congregate into larger compound grains and thus 
render the soil more open in its texture and hence better 
drained and better aerated, as well as more easily and 
thoroughly occupied by the roots of plants. 

But all of these changes which have been referred to 
as resulting from thorough drainage are only means for 
widening and rendering the direct effect of underdrains 
more prompt in their influence and far-reaching in the 
renewal of soil air which they secure. In an underdrained 
field where lines of tile are laid 3 to 4 feet deep and 50 to 
100 feet apart, there is provided a ventilation system 
which operates in an effective manner to hasten the 
change of the soil air. It must be evident that when 



250 The Soil 

the diurnal changes in the temperature of the confined 
soil air and the changes due to alterations of barometric 
pressure are sufficiently pronounced to affect the rate of 
flow of water from tile drains, as has been demonstrated 
in another place, there must also be draining out of a tile 
system, at times of rising soil temperature and of falling 
barometer, considerable quantities of soil air. This must 
be so because, as the soil air expands and pushes upon 
the soil water, forcing it out, some portion of the air 
itself must escape into the drains through their upper 
sides. Then when the temperature falls and the barome- 
ter rises, air will be forced into the soil to take the place of 
that which had been lost, not simply from the surface 
of the ground, but simultaneously along the whole extent 
of the system of underdrains. It is important to recog- 
nize in this connection, that the air which underdrains 
admit to the soil from beneath is in a large measure 
atmospheric air, containing the normal amount of oxygen, 
and since under these conditions the soil can breathe free 
air both from above and below the zone occupied by the 
roots of plants, it is plain that the soil of a tile-drained 
field must be much more thoroughly ventilated than that 
of another entirely similar field having its water table at 
the same distance below the surface and equally open in 
texture, but without tile drains. 

A word should be said regarding the aerating power of 
clover as compared with the similar action of other plants. 
The roots of the red clover being larger than those of 
cereals, and in part fleshy, tend to separate the soil parti- 
cles farther, leaving more effective air passages and drain- 
age channels when they decay than do the roots of wheat, 
oats, barley, or rye. But there is another way in which 
all free-nitrogen-fixing plants help to aerate the soil dur- 



Ways of Influencing Soil Ventilation. 251 

ing their periods of growth. As these withdraw from the 
soil air the free nitrogen it contains and fix it in the solid or 
liquid form, a reduction of air pressure is produced and a 
fresh supply of air must be crowded in to supply this 
deficiency. In so far as other plants work in a similar 
manner to withdraw oxygen and fix it in solid or liquid 
form, without putting in its place an equal volume of 
some other gas, a similar tendency must result, but in a 
less pronounced degree than in the leguminous plants 
which remove both oxygen and free nitrogen. 

Just as the withdrawal of water through underdrains 
forces air to follow it more deeply into the vacated spaces, 
so must the osmotic pressure of all roots, by forcing water 
out of the soil to be evaporated from the leaves, tend also 
to bring fresh supplies of atmospheric air into the soil, 
equal in volume to the water withdrawn. 

It may well be that some soils are so open that they 
are too thoroughly ventilated, just as they are too thor- 
oughly drained. In such cases the decaying organic 
matter is converted into nitrates more rapidly than they 
can be used by the crop, which results in impoverishing 
the soil of its nitrogen store. 

Soils of this type are helped by shallow tillage and a 
thorough firming of all soil except so much as shall be 
needful for a mulch. Keeping such soils thoroughly moist 
diminishes their porosity, as does farmyard manure, which 
tends to clog the pores. 

The loss of the fine dust particles from light soils so 
liable to occur in the spring when the winds are strong is 
a great injury to such lands, both on account of the point 
here under consideration and because the water-holding 
power is greatly decreased thereby, as has been pointed 
out. 



252 The Soil. 



HYGROSCOPIC MOISTURE. 



The moisture which, exists in the air in the form of 
vapor is to a greater or less extent absorbed by soils as 
air enters or comes in contact with the ground during the 
process of soil breathing. The water so taken up by soils 
or other objects is spoken of as hygroscopic moisture. 
Usually the finest grained soils, in the air-dry condition, 
contain more moisture than the coarser grained samples 
do, but the amounts so retained do not appear to hold any 
discovered numerical relation to the amount of such sur- 
face. It is usually more the lower the soil temperature, 
and decreases in quantity as the temperature rises during 
the day. Our knowledge of the laws governing the 
hygroscopic moisture of soils, and of the importance of 
this moisture to plant life, is as yet too indefinite to per- 
mit any very trustworthy statements regarding it to be 
made. There are eminent writers who hold that its im- 
portance, especially in dry climates, is very great, while 
others feel that vegetation can derive but little profit 
from it. 



CHAPTER X. 

FARM DRAINAGE. 

Enough has been said regarding the influence of under- 
drainage on the important matters of soil temperature, 
soil ventilation, and the conservation of soil moisture, to 
show how important this method of improvement may 
be on certain lands. But as land drainage is certain to 
play a much larger part in the future of agriculture than 
it has in the past, it is important that something more 
should be said regarding it. 

We have in the United States, according to Professor 
Shaler's estimate, more than 100,000 square miles of 
swamp lands lying east of the 100th meridian; and these, 
when reclaimed by drainage, are destined to become the 
most productive lands we have. They will be so, not 
only because of the large stores of humic nitrogen which, 
under proper methods of tillage, may be turned into 
forms available to higher plants, but also because they 
lie in humid climates, and are so related to the water table 
that only surplus rains need be lost. Indeed, not only 
can there be no percolation of soil water from these lands 
below the reach of root action; but in very many, if 
not in the majority of instances, they are perennially 
supplied with water through the underflow from the 
surrounding higher land, and are thus naturally sub- 
irrigated. 

That our swamp lands are destined to become rich 

253 



254 The Soil. 

agricultural fields must be evideut when we consider 
that during the 44 years following 1833 the country of 
Holland added to itself lands exceeding in square miles 
the combined area of Rhode Island and Delaware, by 
systems of dikes and methods of drainage so difficult as 
removing the surplus water over the sea barriers with 
pumps. And so fertile are these reclaimed swamp lands 
that nearly 20 years ago there lived on the 12,731 square 
miles, a population averaging, for each square mile, 302 
people, 20 horses, 118 cows, 70 sheep, 12 goats, and 27 
hogs ; and, side by side with this population, there were 
raised 2907 square miles of field crops, exclusive of 
pastures and hay, and the average yearly product of 
these fields between 1871 and 1875 is placed at $45.36 
per acre. 

There are lands other than the swamp areas referred 
to above which may be much improved by draining; 
and it may be said, in general, regarding these that all 
lands will be made more productive by draining where 
standing water in the ground may be found at seeding 
time not more than 4 feet below the surface. All 
very flat areas of fine-textured soil underlaid at four to 
six feet or less with a stratum of highly impervious clay 
or rock, and ponds and slews, as well as springy hill- 
sides, are likely to profit much from a thorough system 
of drainage. 

SOME LARGE DRAINAGE SYSTEMS. 

As an instance of the pains which in some parts of 
this country are now being taken to improve lands by 
underdraining, reference may be made to work which 
is being done in the state of Illinois, where, in many 



Some Large Drainage Systems. 



255 



parts, the fields for long distances are so flat that it is 
difficult to obtain adequate fall or to provide suitable out- 
lets for the drains when laid. Here, in many instances, 
the citizens combine their energies and resources and 
dig broad, open ditches, sometimes many miles in length 
and deep enough to provide suitable outlets for under- 




Fig. 38. — Showing plan of the drainage of lands of the Illinois Agri- 
cultural Company, Kontoul, Illinois. After Professor J. O. Baker. 
The smallest squares represent 40 acres ; double lines show open 
ditches ; single lines are tile drains. 



drains. One such drainage system is found in Mason 
and Tazewell counties. It was begun in 1883 and com- 
pleted in 1886, and has a main ditch 17.5 miles long with 
a width of 30 to 60 feet at the top and a depth of 8 to 
11 feet ; while, leading into this main channel, there are 
five laterals averaging 30 feet wide at the top, and from 



256 



The Soil 



7 to 9 feet deep, the whole system embracing 70 miles of 
open ditch. 

A clearer idea of the character and magnitude of some 
of these drainage systems may be gained from Pig. 38, 
where the double lines indicate open ditches, and the 
single ones tile drains, many of which it was found 
necessary to lay very nearly level. This system was 
begun in 1881 and completed in 1884, and its effect upon 
the total yield of grains of all kinds is stated by Pro- 
fessor Baker as follows : — 



Total yield of grain in 1881, 26,057 bushels. 

1882, 58,647 

1883, 92,360 

1884, 113,660 

1885, 122,160 * 

1886, 202,000 



It is plain from these figures that there has been a 
marked influence following the underdraining in this 
case ; but it should not be understood that the yields per 
acre increased to the extent indicated by the figures, for, 
before the land was drained, there was much of the area 
too wet to be cropped at all, and hence the larger totals 
with successive years are due in part to an increase in 
the acreage. 

It has been pointed out that no lands will produce 
other than swamp vegetation, unless they have first been 
more or less perfectly drained, because, until this is 
done, those biologic processes in the soil necessary to 
cultivated crops cannot be carried forward. They can- 
not for several reasons : the temperature is too low ; 
there is inadequate soil ventilation; and there is an 

* 400 acres of maize destroyed by a water spout. 



Depth of Under drains. 257 

insufficient amount of room in which the roots can 
develop and perform their functions. 

There are two other ways in which imperfect drainage 
works disadvantageously ; first, by preventing early seed- 
ing and thus shortening the growing season and the 
amount of available water and other forms of plant food 
derived from the soil ; and second, besides increasing the 
labor of tillage, it shortens the time in which the work 
can be performed. 

DEPTH OF UNDERD RAINS AND DISTANCE BETWEEN 

THEM. 

The depth to which the water should be lowered by 
drainage, below the surface of the ground, need seldom 
exceed 4 feet for ordinary farm crops, while under 
some conditions the lowering of the water table may be 
less. We have many cases on springy hillsides and on 
flat areas between rises of ground, where the water is main- 
tained within 4 feet of the surface for only a short 
period in the spring. In instances like these, where the 
water table falls normally 5 to 7 feet below the surface 
as the season advances, it is only necessary to insure a 
sufficient drying of the surface 18 inches in which the 
plants may begin their growth. When this is done, 
the gradual fall of the water table as the crop grows 
allows the subsoil to become sufficiently dry and open 
through the natural process of drainage and evaporation 
from the surface. Where such lands are deeply tile 
drained, there is liable to be a needless waste of much 
water. 

In sandy soils, too, and others which are naturally 
leachy and open, it is not as important to draw the ground 



258 



The Soil. 



water down as low as when the soil is more close and 
impervious in texture. But in all cases where the water 
table usually remains as near the surface as 4 feet during 
the whole summer, the drainage system should be planned 
to draw the water down at once to from 3.5 to 4 feet below 
the surface, and hold it there. 

There are times when the ground lias become very 
dry, and especially when the soil is a stiff clay and has 
checked to a large extent as the result of drying, when 
heavy rains come they percolate so rapidly into the sys- 
tem of tiles that a large share of the water is lost before 




Fig. 39. — Showing how the distance between drains affects the depth 
of drainage. With drains at A and C the water will be highest 
at B ; but with drains at A, D, and C the surface of the ground 
water will be more nearly the line AEDFC. 



it has time to be absorbed by the soil. In such cases, 
although no provision is usually made for it, the writer 
feels that, were tile drains provided with a few valves at 
different places in the system, which might be closed at 
such times and thus retain the bulk of the water for 
a day or more, until sufficient time has elapsed for the 
water to be taken up by the capillary pores of the soil, 
no inconsiderable advantage would be derived from it. 
The writer has seen, on three different occasions when 
a heavy rain has followed a dry period, that on tile- 
drained ground a very large part of the water was lost 



Depth of Underdraiyis. 



259 



through the drains when the soil was much in need of 
more than had fallen. 

The distance between underdrains will vary with the 
closeness of the soil texture and the depth at which they 
are laid. Since the water table rises as the distance 
from the outlet increases, it is plain that midway be- 
tween lines of tile the surface of the ground water must 
approach nearer to the top of the ground, and the nearer, 
the farther the lines of tile are apart, as illustrated in 
Fig. 39. 

The actual contour of the water table in an under- 




Fig. 40. — Showing the observed surface of the ground water in a tile- 
drained field 48 hours after a rainfall of .87 inches. 



drained field, where the lines of tile are placed at dis- 
tances of 33 feet and 4 feet below the surface of the 
ground, is shown in Fig. 40, which gives the contours 
as they existed 48 hours after a rainfall of .87 inches. 
In this case the height of the water midway between the 
lines of tile varied from 4 inches to 12 inches above the 
tops of the tile, and the mean rate of rise was 1 foot in 
every 25 feet ; that is to say, in soils of this character, 
when the drains are laid 50 feet apart, the water may 
stand in the ground midway between the lines 1 foot 
nearer the surface than the tiles themselves 48 hours 
after such a rain ; -and if 100 feet apart, then 2 feet nearer 



260 The Soil. 

the surface of the ground. In well 29, Fig. 21, situated 
150 feet from the lake, and hence from the drainage out- 
let, the water stood on June 27, 1892, 7.214 feet above 
the lake level, thus showing a rise of 1 foot in every 
24.4 feet ; but later in the season, when the ground had 
become drier, the level had fallen until the rise was 1 
foot in 35.86. As this slope occurred in September, when 
percolation from the surface had long since ceased, it 
may be regarded for such soil as a minimum gradient. 
Taking the rise as 1 foot in 36 feet, lines of tile 72 feet 
apart and 3 feet deep would allow the water table to rise 
to within 2 feet of the surface along a line midway 

between the drains. 

i 

SUB-IRRIGATED LANDS. 

Just how quickly the water table may be drawn down 
after a rain by a system of tile drains is shown in Fig. 
41, where the broken lines represent the surface of the 
ground water on May 12, 13, and 16, the latter date 
being 5 days after a rainfall of .87 inches. It will 
be seen that the changes in level of the water table were 
very far from being uniform in different parts of the 
field, the fall being fastest under the highest ground, 
where it passed entirely below the upper three lines of 
tile. In this case, as indicated by the arrows, the lower 
portion of the field is subject to sub-irrigation, the water 
under the higher ground tending, through its greater 
hydrostatic pressure, to move toward and up into the 
soil of the lower field. 

Sub-irrigated lands of this character occur in many 
places and under conditions where the geological struc- 
ture is much as represented in Fig. 42. In these cases 



Sub-Irrigated Lands. 



261 



the surrounding high lands are more or less open in 
texture, so that the rains percolate into them readily, 
but drain away slowly, making the adjacent flat lands 
more or less springy or marshy, and only fit for tillage 
after they have been underdrained. Such lands, however, 
once they are underdrained, become very valuable on ac- 
count of their abundant water supply. Nor is this type of 
land at all uncommon in the northern part of the United 
States. Indeed, the glacial hills referred to in an earlier 
chapter are impounding reservoirs of great extent and 
capacity, into which the rains sink immediately, and are 





1 Z J. 4 S. <>. 7. 




























May. 

IZWI 
13, UM 


































A ^V 






.... 


ZZZ£~-~' 


s== 


=== 


=2= 


._. 


:::.' 


— ■••—•' 




■•ZZTZZZ^Zr 2 ?' ""Tlrt 


[.•■TV 




\ 


' 








fJlaU 


% ■*"» 























Fig. 41. 



Showing the rate of change in the level of the ground water 
after a rainfall of .87 inches. 



there stored, under conditions of least possible loss by 
evaporation, to be given out gradually in restricted but 
innumerable areas. Heavy rains which in countries of 
different structure are lost to agriculture in disastrous 
floods are here safely and economically stored ; and it is 
to this stored water escaping slowly again from the 
ground, more than to direct rainfall and flat topography, 
that we owe the existence of our innumerable small 
lakes, and the many areas of swamp and lowland pas- 
tures so characteristic of glaciated regions. These many 
naturally sub-irrigated tracts are especially promising for 
market gardening and other forms of intensive farming. 



262 The Soil 

There is another phase of this question to which atten- 
tion should be called. There are many and extended 
tracts of country underlaid by artesian waters, where 
water. can be had at the surface whenever the overlying 
impervious strata are penetrated. Now, in view of the 
fact that the best of Portland cements are not wholly 
impervious to water, even under moderate pressures, it 
may also be true that in many parts of artesian districts 
there is a slow, upward penetration of the deeper waters 
into the field soils, which possibly contributes not a little 
to the natural productiveness of such lands. 



~* " ' ■ '•''~' w -~-'~ i ~t ^~ ■ •*-"•' - . " r ~- B&a&aa T* 1 " tsi — ^T'~r , r^ ■ i~^ . t~~- ' "' ^7i "^i ^ >? r, wT'n — i 



Fig. 42. — Showing the geologic structure favorable to natural sub- 
irrigation. 



SURFACE DRAINAGE. 

Where extensive flat fields of very fine-textured, im- 
pervious soils occur, it is often desirable, and even neces- 
sary, to adopt some form of surface drainage. There 
are some clayey soils in their virgin state which are so 
impervious to water that it would be useless to lay 
drains deeply in them, even were the lines near to- 
gether, because the water would percolate into them too 
slowly to render them efficient. In such cases surface 
drainage must be resorted to. This is done by plow- 
ing the fields in narrow lands, leaving dead furrows 



Surface Drainage. 263 

extending in the direction of the natural slope, and from 
20 to 60 feet apart. Where the lay of the land makes it 
necessary to do so, the dead furrows may be connected 
by cross furrows, in order to lead the water away 
through some low place. 

It is often desirable, even where underdrains are used, 
to have some surface drains to carry away surplus water 
in times of freshets. Such ditches are best made wide 
with very sloping sides, so as to be grassed over and to 
permit a team and wagon to be driven across them at 
any place. 

The Celtic land beds of olden times represented an 
effort to secure deep drainage with surface or open 
ditches. Marshall, writing of this method of land im- 
provement in 1796, says that the ridges of that time were 
8 yards wide and from 2 to 2.5 feet high, but he meas- 
ured some which were 15 yards wide and 4 feet high, 
while others were 20 to 25 yards wide, and so high that 
a horseman riding in one ditch could hardly see his com- 
panion riding in the other. This method of drainage 
must be very wasteful of land, and is only to be resorted 
to when, for any reason, covered drains cannot be made. 

There are many depressions or low places which, on 
account of being surrounded on all sides by higher land, 
cannot be made dry either by surface or underdraining. 
It is frequently true of such cases that the water is held 
by a pan of clay which has been formed from washings 
from the higher ground, while under this pan the soil 
is open and capable of readily carrying the water away. 
When this is true, and the area which drains into the 
basin is not too large, it may be drained by boring or 
digging through the clay in one or more places, making 
exits for the water to escape by percolation downward. 



264 



The Soil 



These drainage ways may be kept open, or they may be 
filled in with coarse stone, sand, and gravel. 

When the clay is too deep to permit of draining in 
this way, the result may be accomplished, if the amount 
of water to be removed is not too large, by sinking a 
well or reservoir of considerable size at the lowest place, 
into which the drains lead from various directions. This 
water may then be lifted by wind or other power, and 
used to irrigate grass or other fields bordering the wet 




Fig. 43. — Showing the drainage system of 80 acres in northern Illinois. 
After C. G. Elliott, C.E. Double lines represent mains ; single 
lines are laterals. Numbers give length of drains and size of tile. 

area, thus getting rid of the water by evaporation and 
making it do service at the same time. 



COST AND ARRANGEMENT OF UNDERDRAINS. 

We cannot in this place discuss the practical details of 
underdraining, but as an illustration of the method of 
distributing and joining main drains witl* laterals, we 
have selected an actual piece of work done where a 
farm of 80 acres in northern Illinois has been drained 



Cost and Arrangement of Underdrains. 265 



under the supervision of Mr. C. Gr. Elliott, C.E. The 
land he describes as a rich black loam, approaching muck 
in the ponds and flats, underlaid with a yellow clay sub- 
soil at a depth of 2.5 feet from the surface. In draining 
this piece the object has been to fit it for growing corn, 
grass, and grain in all seasons, and it will be seen (Fig. 
43) that the laterals are, where nearest, about 150 feet 
apart ; but it should be understood that the aim has not 
been to provide perfect drainage, but rather as good as 
would pay a fair interest on the money invested where 
general farming is practiced. 

The fall of drains should not be less than 2 inches 
per each 100 feet when it is practicable to secure this 
amount. A smaller fall may, if necessary, be used, but 
more is better. In the field represented by the figure 
the main drains have a fall of 2 inches per 100 feet, and 
the laterals more rather than less. 

I give below the cost of doing this piece of work with 
the items as stated by Mr. Elliott. 

COST OF MAIN DKAINS PER 1000 FEET. 



No. OF 
Feet. 


Size. 


Depth. 


Tile. 


Digging, 
Laying, 

AND 

Filling. 


Total. 


Cost per 

PwOD. 


1000 


7 in. 


5 ft. 


$60.00 


$37.20 


$97.20 


$1.60 


2700 


6 in. 


5 ft. 


40.00 


36.60 


206.82 


1.26 


850 


5 in. 


4 ft. 


30.00 


24.20 


46.07 


.89 






COST OF LATERAL DR^ 


JNS. 




8280 


4 in. 


3.5 ft. 


20.00 


20.00 


331.20 


.66 


7030 


3 in. 


3 ft. 


13.20 


20.00 


233.40 


.55 




Total . 


. . . 


$914.69 





The total cost of $914.69 makes an average per acre of 
$11.43. 



266 



The Soil. 



It will seldom be best to use tile smaller than 3 
inches, and in laying them great care should be exercised 
to place them on a true grade, because if the lines of tile 
have high and low places in them, whose differences 
exceed the diameter of the tile, silt will tend to collect 
in the low places and sooner or later close them up. 

The outlet of a drain should be carefully made and 
end above water as represented in Fig. 44. If the out- 
let is below standing water, the silt which is brought 
down tends to close up the main, and thus render the 
whole system useless. So, too, when a lateral is led into 




tlD 




Fig. 44. — Showing proper and improper outlets of drains. A, proper 
outlet; B, improper outlet ; C, proper junction of lateral with 
main; D, improper junction. 



a main the union should be made at an angle as at C 
rather than as at D. 

Care must always be exercised to remove water-loving 
trees from near lines of underdrains, lest their roots 
penetrate the joints and there branch into a vast network, 
entirely filling the tile, when, by retaining the silt brought 
by the water, they will sooner or later completely close 
up the tile. Fig. 45 represents a mass of roots thus 
formed in a tile drain. These roots are those of the 
European larch, and they penetrated a main drain at a 
depth of 5 feet below the surface, the trees standing at 



Cost and Arrangement of Under drain*. 267 

a distance of 15 feet from the line. As will be seen, the 
roots, after entering the main, branched into a great 
system of fibres, which effectually closed a 6-inch drain, 
making it necessary to take np the line of tile in that 
vicinity. 




Fig. 45. — Showing the roots of European larch removed from a 6-inch 
tile drain, which they had effectually clogged. 



CHAPTER XI. 

IRRIGATION. 

Reference was made in the last chapter to the large 
acreage of lands now lying idle and practically worth- 
less, so far as the needs of civilization are concerned, 
which have yet to be Avon to remunerative agriculture 
through a judicious application of methods of drainage ; 
and to still other lands which may be made more produc- 
tive than they now are through, the same means. 

It is not the purpose here to speak of methods of irri- 
gation in detail, nor of irrigation as applied to arid and 
semiarid regions, because there its value is appreciated 
and needs no enforcement; but rather to consider in 
a general way the great promise it has for lands receiv- 
ing moderate amounts of rain during the growing season. 
This is done because we are fully persuaded that the 
maximum limit of productiveness of lands in humid 
regions can only be attained through a suitable combina- 
tion of both drainage and irrigation. Further than this, 
there are many hundred square miles of light lands lying 
east of the Mississippi, which are now almost as unproduc- 
tive as the undrained swamps are, but which irrigation, 
properly handled, would cause to bloom into the richest of 
gardens. The rainfall of the eastern and central United 
States is so capricious, the amount of water needed for 
large yields so great, and the difficulties in the way of 
making our soils retain enough of the water which falls 

268 






Irrigation in Humid Climates. 269 

to meet the demands are so many, that it must be plain 
to every practical man and student of agriculture, who 
has devoted much thought to the subject, that the time 
must come when the waters now running to the sea, 
with their tons of unused fertility, will be turned to 
use in irrigating many of the fields through which 
they flow. 

IRRIGATION IN HUMID CLIMATES. 

The advantage of irrigating lands in humid climates 
has been abundantly proved by long trial in many 
parts of the world, and it is the object here to call 
attention to the facts and to point out a very important 
and remunerative channel in which American capital 
should seek investment. If it will pay to irrigate in 
arid climates, where all the needed water must be sup- 
plied under conditions of cost far exceeding what will 
be needed in humid districts, there must certainly be 
many lands near large markets and close to water which 
can be irrigated with great profit. 

In illustration of what sewage irrigation is doing in 
Scotland, the statements of Storer, made after visiting 
the irrigated meadows near Edinburgh, may be cited. 
He says : — 

" In 1877 there were 400 acres of these ' forced mead- 
ows ' near Edinburgh, and they are said to increase 
gradually. The Craigentinny meadows, just now men- 
tioned, were about 200 acres in extent, and they had been 
irrigated for thirty years and more. They were laid down 
at first to Italian ray grass and a mixture of other 
grass seeds, but the artificial grasses disappeared long 
ago, couch grass and various natural grasses having 



270 The Soil. 

taken their place. The grass is sold green to cow 
keepers, and yields from $80 to $150 per acre. One 
year the price reached $220 per acre. They get five cuts 
between the 1st of April and the end of October. This 
farm of 200 acres turns in to its owner every year from 
$15,000 to $20,000 at the least calculation, and his run- 
ning expenses consist in the wages of two men, who 
keep the ditches in order. The sewage he gets free. 
The yield of grass is estimated at from 50 to 70 tons 
per acre. The total produce of the sewage irrigation 
at Edinburgh amounts to at least $30,000 per annum, 
taking one year with another. The grass goes to some 
2000 cows, and the milkmen all acknowledge that they 
cannot get any milk-producing food to compare with 
it for the same amount of money, notwithstanding the 
seemingly high price that is paid for the grass per 
acre. Of course the dung from these cows goes to 
fertilize other farm land." 

The lands from which these large returns are being 
realized are described as having been a worthless, sandy 
waste previous to their improvement by sewage irrigation. 

Referring to results obtained on the Myremill farm 
of 508 acres near Maybole, in Ayrshire, Scotland, John 
Wilson quotes at length from the " Minutes of Informa- 
tion" issued by the General Board of Health, to the 
effect that some 400 imperial acres were laid down to 
iron pipes placed from 1.5 feet to 2 feet below the surface, 
and provided with hydrants at intervals, to which hose 
are attached for the distribution of the water contain- 
ing the fertilizers. In this case the water used in irri- 
gating the farm was lifted 70 feet with pumps driven by 
a 12-horse-power engine and stored in large reservoirs, 
the cost of which, including pipes and hose, is placed 



Irrigation in Humid Climates. 271 

at $7676. Counting 7.5 per cent on this sum, for interest 
and wear and tear, and a working expense in distribu- 
ting the water of $786.50 per annum, the total annual 
cost of irrigation equals $1362, or $2.68 per acre. The 
land laid down to grass is said to have produced 70 
tons of green weight per acre, so that at this rate the 
70 acres in Italian ray grass gave a gross crop of 4900 
tons, and the market value of this one crop of meadow 
grass exceeded, by a large sum, the first cost of the 
irrigating plant. It is said that this same land before 
being treated in the manner described would barely 
pasture 5 sheep or 1 bullock to the acre, but under 
the irrigation system it was easy to keep 20 sheep or 
5 bullocks to the acre by hurdling and moving from 
place to place. 

Fabulous as these results appear, fourteen other cases 
are cited by the same author, and they all have the 
same import. To illustrate: In one case a weighed 
crop of 10 tons per acre of ray grass was taken, and 
this is said to be the lightest of four cuttings in one 
season. In another, where 12 stacks per annum were 
formerly taken, now 80 are obtained. And again where 
the yield was worth $1 per acre, it is now $58. 

It should be understood that all of the cases here 
referred to are looked upon as methods of manuring 
the land, that is, fertilizers are added to the water and 
with it distributed over the fields ; but there can be no 
question but that the larger yields secured are due 
much more to the water than to the fertilizers added 
to it, or more exactly to a proper combination of both 
rather than to either one of them alone. 

In proof of the possibilities of obtaining very heavy 
yields of dry matter per acre, it may be stated that the 



272 The Soil. 

writer grew, under field conditions in 1894, by irrigating, 
14.5 tons of dry matter to the acre on -jL of an 
acre of ground, when the crop was a variety of flint corn. 
The ground upon which this maize was grown was a 
clover sod, well fertilized with a dressing of farmyard 
manure, and the same ground Avith the same variety of 
maize gave less than 4 tons to the acre where only the 
natural rainfall was available. 

The irrigation of grass lands has been widely practiced 
in Europe and for a long time. For pasture land and 
meadows the system is in use in Germany, Switzerland, 
France, Spain, and in many provinces of Italy. We are 
told that in 1856 the old kingdom of Sardinia had 
600,000 acres of land under irrigation; in Lombardy 
there were 1,100,000 acres and 300,000 in France. Marsh 
states that two canals in Lombardy, which now irrigate 
some 250,000 acres, were dug in the twelfth century. 
Palestine and Persia are noted for the extensive and 
highly perfected systems of irrigation which brought 
wealth to those countries in the days of Babylonian 
greatness, but which are now in utter ruin. So, too, in 
Ceylon the native rulers in ancient times covered the 
whole face of their island with a network of irrigation 
reservoirs, through which Ceylon became the great gran- 
ary for southern Asia, but through the devastation of 
wars they have long since passed into ruins, and it is said 
that what were once highly productive irrigated fields 
are now swampy wastes or dense forests. 

Even in Mexico and Peru, the Spaniards brought 
destruction to elaborate systems of irrigation, as they 
had done before to those in their native land which had 
been built in the sixth century by the hands of the 
thrifty Moors, 



Cost of Irrigating. 273 

H. M. Wilson, in speaking of the extent of irriga- 
tion, places the acreage in various countries as follows : 
Total area irrigated in India, 25,000,000 acres ; in Egypt, 
6,000,000 acres ; and in Italy, 3,700,000 acres. In Spain 
there are 500,000 acres, in France 400,000, and in the 
United States 4,000,000, acres of irrigated land. In 
addition to this, he states that there are some millions 
more of acres cultivated by the aid of irrigation in 
China, Japan, Australia, Algeria, and South America. 

COST OF IRRIGATING AND AMOUNT OF WATER USED. 

The amount of water used in irrigating is very large, 
as indeed it must be when large fields are to be dealt 
with. In Italy often as much as 4 inches of water on 
the level are applied to the meadows at a single wetting, 
and amounts equivalent are applied at intervals of ten 
days or two weeks, varying of course with the weather ; 
but it usually happens, in these cases, that a considerable 
portion of the water passes beyond the field to which it 
is directly applied and is utilized on lower lying areas. 
Smith concludes from statistics in India that there 
1 cubic foot of water per second is sufficient for 180 acres 
of land where the water is used the whole year through, 
and this is equal to 48 inches on the level. Five esti- 
mates of the amounts of water required in French and 
Italian experience for water meadows, where the period 
of consumption is about half the year, gives an average 
of 86 acres of land watered by a continuous flow of 1 
cubic foot per second, and this amounts to covering the 
ground with a depth of water equal to about 50 inches, 
the water being used from the middle of March to the 
middle of September. This is a very large amount of 



274 The Soil. 

water when considered in connection with the natural 
rainfall, amounting to from 20 to 40 inches, but it must 
be observed that three and sometimes four crops of 
grass are cut from the land each season, besides using it 
for pasture in the fall. 

In obtaining water for irrigation purposes, there are 
many methods which may be used and are to-day in use 
in various parts of the world. The most natural method, 
where the topography of the country will permit of it, 
is to lead the water out from some point up stream into 
irrigating canals, which convey the water to flat lands 
farther down. Or various forms of lifting wheels are 
placed in the stream, and considerable quantities of water 
are raised by them and discharged into side channels. 
Hydraulic rams are used and a great variety of pumps 
driven by steam or other power. Using a No. 4 rotary 
pump driven by an 8-horse portable farm engine, the 
writer has drawn water through 110 feet of 6-inch suc- 
tion pipe, raising the water to a height of 26 feet, at the 
rate of 80,320 cubic feet per ton of soft coal, which is 
equivalent to 221 inches of water per acre, or over 7 
acres covered to a depth of 3 inches. But this amount 
is much less than could have been moved with the 
same fuel had the pump been provided with a larger 
discharge, and could the water have been used as rapidly 
as pumped, so as to have made frequent stops unneces- 
sary. Windmills may be used to advantage in many 
cases where the lift is small', where the area to be 
watered is not large, and particularly where reservoirs of 
considerable capacity may be used for storage. 

While it is true that much profit may be realized 
through irrigation in humid climates on a small scale, 
yet the largest returns can be secured only when a con- 



Cost of Irrigating. 275 

siderable capital is involved, but this is no argument 
against the development of the system, provided the 
income is sufficient to keep the capital profitably em- 
ployed. 

The cost of irrigation west of the 100th meridian in 
the United States, as given in the United States census 
for 1890, averages $8.15 per acre for the construction 
of canals to bring water to the land, while the average 
value of the water per acre, when once there, is placed 
as high as $26, but the average annual cost of water 
per acre is $.99. The value of the lands before irriga- 
tion improvements were added is placed at from $2.50 
to $5.00 per acre, but after the water was added to it 
the same lands are valued at $83.28 per acre. 

To show what has been done on barren sands in 
Belgium, it may be stated that 5636 acres of sand dunes 
have been reclaimed by irrigation, under government 
control, and that these lands yield 6615 pounds of hay 
per acre, with an aftermath valued at $2.00 per acre, 
which, with the hay, gives an income placed at $29.93 
per acre. 



CHAPTER XII. 

THE PHYSICAL EFFECTS OF TILLAGE AND FER- 
TILIZERS. 

The great importance of good tilth has always been 
appreciated by thoroughgoing practical men, and ex- 
perience has abundantly taught that the stirrer and 
more resistant the soil, the greater should be the care 
and attention given to the field to bring it into perfect 
tilth before receiving the seeds or plants which it is 
expected to bring to maturity. 

But Nature neither plows, harrows, nor hoes her fields, 
and yet where water is abundant and the temperature 
right, the grasses thrive, the flowers bloom and fruit, and 
tree and shrub vie with one another for the occupancy 
of the whole surface of the earth even to vertical, rocky 
cliffs and steep mountain sides. Why, then, should tilth 
be so important a matter in successful farming ? 

When we reflect upon Nature's methods, we see plainly 
that they are quite different from those adopted by thrifty 
husbandry. In the first place, by Nature's method's, not 
one seed in many hundreds ever germinates and comes to 
maturity, but in farming no such chances can be taken. 
Conditions must be favorable not only for every seed to 
germinate, but also for each plant to come to full matur- 
rity and bear fruit. In the second place, by Nature's 
methods, almost all fields bear a mixed vegetation, and 
her rotations are maintained by slipping in a different 

276 



The Importayice of Good Tilth. 277 

plant where the accidents of life, or death from age, have 
left vacant places ; but in agriculture certain crops must 
occupy the field for the season to the exclusion of all 
others, and in these differences in aims and methods we 
find the chief needs for, and the great importance of, 
good tilth and thorough tillage. 

THE IMPORTANCE OF GOOD TILTH. 

From what has been said regarding the thorough oc- 
cupancy of the soil by the roots of our cultivated crops, 
penetrating as they do three and four feet into the stiff 
clay subsoils, which have never been stirred, it may 
seem that a mellow seed bed should have no significance 
so far as the growth and spread of roots are concerned. 
Practical experience, however, proves beyond question 
that a mellow seed bed is important, and a little reflec- 
tion will make it clear why it must be so. 

In the first place, when seeds are beginning to grow, 
or when sets are transplanted into a new soil, there is 
yet no organic connection between the plant and the soil 
upon which it must depend for the supply of indispen- 
sable moisture ; both the plant in the seed, and the set, 
have limited stores of nourishment which can be devoted 
to the development of a root system, placing that in vital 
connection with the soil grains, and these stores must 
be used up quickly, once the draft upon them has been 
begun; for, if they are not, pathogenic changes set in, 
which result in their destruction and the death of the 
seed or the set. Now, if the seed is placed under con- 
ditions where it finds many obstacles in the way of a 
free and symmetrical development of the first roots, it 
loses time and food is wasted in getting so connected 



278 The Soil. 

with the soil as to be able to feed itself. A mellow seed 
bed, with its many well-aerated pores, allows the roots 
to grow unhindered in any and every direction, and to 
place their absorbing surfaces in vital touch with the soil 
grains and soil moisture. In this way the nourishment 
in the seed produces the maximum root surface in the 
shortest time, which is an evident and great advantage. 

In the second place, our methods of tillage tend inevit- 
ably to so alter the texture of the surface soils, especially 
if they are heavy, as to make the spread of young roots 
through them more difficult, and hence thorough stirring 
for tilth becomes more important than it was in the vir- 
gin state. The frequent stirring tends to break down 
the compound grain structure, so that the action of rains, 
and of stirring when too wet, causes the soil grains to 
run together into masses of so close a texture that the 
young roots find difficulty in making their way among 
them, and are insufficiently supplied with air even if they 
succeed in doing so. It is this physical change forced upon 
heavy clay soils which makes it so essential that they be 
laid down frequently to grass and given time for bring- 
ing together again into compound grains the minute 
particles which frequent tillage tends to separate, and 
which the rains cause to run together into masses of 
close texture. 

The perfect tilth and freedom from clods so character- 
istic of virgin soils, is always more or less completely re- 
stored whenever soils have been laid down to grass for a 
sufficient length of time. After they are covered with 
sod, the puddling action of rains is prevented, and, as the 
roots grow and decay, the soil particles are wedged apart 
in some places and crowded together in others. Then 
the solvent action of carbon dioxide in the soil water re- 



Management of Soil to Secure Good Tilth. 279 

suits, through the deposit of the dissolved lime or other 
materials, in cementing together the grains and in restor- 
ing the more open and mellow texture characteristic of 
virgin soils. It is plain from these facts that the laying 
down of land to grass at frequent intervals is beneficial 
in other ways than that of increasing the stores of cer- 
tain kinds of plant food, and rotation of crops is seen to 
have a significance in the good influence it has upon soil 
texture. 



MANAGEMENT OF SOIL TO SECURE GOOD TILTH. 

When stirring soil to improve its texture, the amount 
of moisture present at the time plays a very important 
part in the final result. If water enough is present to 
nearly or quite fill all the capillary spaces, leaving no 
free water surface upon which surface tension can come 
into play, then the individual soil particles move over 
one another with the least resistance, and a little pres- 
sure or stirring at such a time causes them to slip into 
all large empty spaces and to assume the most compact 
arrangement possible, but one very unfriendly to the 
normal life processes going on in the soil. When the 
amount of water becomes less, however, so that free 
water surfaces are formed in all the larger non-capillary 
pores, then surface tension comes into action, tending to 
bind the particles of the compound soil grains and smaller 
shrinkage lumps together, and plowing or otherwise stir- 
ring the soil in this stage causes it to crumble and assume 
that open texture so much sought 'for by those who ap- 
preciate the importance of good tilth. 

It sometimes happens, however, to clayey soils, which 
are naked, that they become excessively wet through 



280 The Soil. 

drenching rains, and if, under these conditions, hot, drying 
winds follow, so that water is evaporated from the sur- 
face rapidly, an internal stress or strain is set up, which 
tends to force the soil grains into the places vacated by 
the water. Now if the drying is very rapid at the time 
when the soil grains float together most easily, that is, 
when the 5 or 6 inches below the surface the soil is nearly 
full of water, then certain spots which, for any reason, 
chance to be more resistant than others, come to be 
centres toward which the surrounding soil grains begin 
to move under the pull of surface tension, like the walls 
of a soap bubble, and cracks are formed bounding large 
blocks of soil, which are forming into clods. The width 
of the cracks shows how much the internal pore space of 
the blocks has been reduced, and how much the texture 
of the soil is being injured by the destruction of needed 
passage ways. 

But if the drying after such wet times is slow, giving 
time for the water to drain away as well as to evaporate, 
then the soil moves upon itself with more difficulty, and 
the effect of surface tension is to cause shrinkage about 
very many rather than a few centres, and the formation 
of large clods is averted. This being true, it is plain 
that the formation of large clods under the former con- 
ditions may be prevented by stirring the surface just as 
soon as the ground is dry enough to permit this to be 
done. Stirring the surface, as with a harrow or culti- 
vator, at such times operates in two ways to prevent 
the shrinkage into large blocks. It lessens the loss of 
water at the surface, and thus gives more time for drain- 
age before much drawing together has taken place, and 
also by cutting or scratching the surfaces of large blocks 
which have begun to form, they tend to divide it into 



Management of Soil to Secure Good Tilth. 281 

smaller sections on account of weakening due to the sur- 
face cutting. 

So, too, if the ground is plowed at such times, as soon 
as the soil is dry enough not to puddle, then, as the 
furrow slice is bent and doubled upon itself, it tends to 
divide into innumerable layers, which, in shearing over 
one another, break and pulverize any clods which have 
commenced to form. This shearing or pulverizing action 
of the plow will be seen at once, if the reader will close 
this book and bend its leaves abruptly upon themselves. 
As this is done, it will be observed that each leaf slips 
past or upon the other. Just so it is with the plow, 
and the steeper the mold board, that is, the more 
abruptly the furrow slice is bent, the greater is the pul- 
verizing effect; and it follows from this, that soils natu- 
rally hard should, as a rule, be plowed with a steeper 
plow than is necessary or desirable for the lighter and 
naturally mellow lands. 

If the leaves of this book were all glued rigidly 
together, so that one could not slip upon the other when 
bent, then no shearing would take place; but under 
sufficient force, the leaves would break. So, too, with 
the furrow slice; if the soil has become too dry before 
plowing, the shearing or pulverizing effect of the mold 
board is prevented, and the furrow simply breaks into 
larger or smaller lumps, instead of small crumbs; and 
not only is a poorer quality of work done, but more 
energy must be expended to do it. It is evident, there- 
fore, that those who have stiff clay soils to work need 
to exercise great judgment regarding the condition the 
soil is in when it is stirred, and these remarks apply to 
harrowing and cultivation as well as to plowing. 

In the case of corn ground, if a heavy rain has fallen 



282 The Soil. 

upon clay land after the crop is planted, great effort 
should be made to stir the surface of that soil just as 
soon as the team can walk upon it without sinking into 
it more than 1 to 1.5 inches, and the heavier the soil, 
the more important it is that just the right moment be 
seized upon. If a light harrow is used in such cases, so 
that a very shallow surface layer is moved, it is surpris- 
ing to see how soon after a rain such land may be stirred, 
and how helpful this slight stirring is in preserving the 
open, mellow texture as well as needed moisture. It is 
at such times as these that very shallow cultivation for 
heavy soils is specially to be recommended, but to be fol- 
lowed by deeper stirring as soon as the ground is drier. 

We have already pointed out how important good 
tilth is in securing the right temperature, adequate soil 
ventilation, and less loss of water by evaporation. 

From what has been said here, and in other places, it 
follows that subsoiling for the sake of improving texture 
will be desirable only in special cases. Well-drained 
subsoils, which have been long under the influence of 
vegetation and the action of burrowing animals, like the 
earthworms and ants, appear to have become sufficiently 
porous to meet the demands of most crops in humid 
regions, so that deeper tillage than that needful to set 
a crop fairly upon its feet is unnecessary. The depth 
of surface tillage, for the sake of texture, should vary 
somewhat with the crop, soil, and season. Where crops 
with fleshy roots are to be grown in heavy soils, it 
becomes specially important to secure an open texture 
in order that the rapidly expanding tubers may find it 
not too difficult to crowd the soil aside and make room 
for themselves, and it is the difficulty in maintaining a 
sufficiently yielding soil on the heavy clay, which makes 



Burning and Paring. 283 

hill or riclge culture preferable many times to the level 
tillage more generally used on the loose, friable lands. 

In the semiarid regions, where irrigation is not prac- 
ticed, and where the soil is fertile to considerable depths, 
deep tillage, preparatory to seeding, and deep planting 
are sometimes desirable to produce a texture so open 
that the scanty rains may enter the soil deeply and at 
once, in order that it shall not be lost by surface evapo- 
ration, and that capillarity shall not return too much 
water to the surface, as has been referred to. In such 
cases the deep, open texture and methods of listing 
allow seeds and roots adequate ventilation with a likeli- 
hood of more water. 

The texture of clayey soils, when fall plowed and 
exposed to winter freezing, becomes sensibly altered and 
usually for the better, a more crumbly and friable char- 
acter being the result. As the soil water in wet clays 
freezes, it is withdrawn from the interspaces to a con- 
siderable extent, and built into crystals of varying sizes, 
among the soil grains, in such a manner as to fissure and 
crumble the clay, and if in the spring drenching rains 
do not undo, by puddling, the action of the ice crystals, 
the soil is left more open. 

It is not improbable, however, that the action of 
carbonic acid, in its tendency to flocculate the colloidal 
clay, may play a very important, if not the chief, part 
in transforming the cold, obstinate disposition of these 
soils into a more friendly nature during the winter 
weathering. 

BURNING AND PARING. 

It has been a common practice in some countries to 
improve the texture of heavy clay soils by burning, and 



284 The Soil. 

the allied operation of paring and burning had, at one 
time, an even more extended use. 

Properly burnt clay loses its plastic quality and falls 
easily into a light, friable powder, and those clays which 
contain silicate of potash, with some carbonate of lime, 
are most improved by the process. 

It is essential in the burning of clay that it be not 
allowed to pass much above a dull red heat; for other- 
wise it becomes hard and brick-like and loses its chemi- 
cal vigor to a large extent. When so treated, clay loses 
its power of again becoming adhesive when wet, while it 
apparently imparts the same quality to a considerable vol- 
ume of that which has not been burned, thus giving to the 
whole a much more open texture and less adhesive quality. 

It has long been known to the arts that raw clay is 
not easily acted upon, even by strong acids, and so in the 
manufacture of chemicals the inert clay is exposed for 
some time to a dull red heat, and in this process it 
comes to be readily acted upon by sulfuric acid in the 
operation of alum making. Whether the burning has 
any other effect than to destroy the colloidal clay, and 
thus render the mass easily penetrated by the acids, and 
hence more readily acted upon, does not appear to be 
well understood. But it is true that the clay becomes 
much more porous, more easily worked and attacked by 
chemical agents; and these are valuable qualities in any 
agricultural soil. In burning clay, it is usually mixed 
with brushwood or peat or sometimes with soft coal. 
To better control the operation and hold the fire in check, 
long, narrow trenches are sometimes dug and then filled 
in with alternate layers of brushwood and clay and, 
after being fired, more clay and fuel added as the burn- 
ing proceeds. 



Texture of Soils Influenced by Fertilizers. 285 

The allied process of paring and burning seems now 
to have largely gone out of use, though in parts of Europe 
it was quite general on certain lands. It consisted in 
shaving off 1 to 3 inches of the surface soil with its 
sod or stubble and gathering it together into heaps to be 
burned, when dry enough, with the aid of the roots, 
stubble, and other organic matter it may have contained. 
The process was, of course, attended with considerable 
losses of nitrogen, and hence was wasteful besides being 
laborious and costly, but it did produce marked beneficial 
effects on many soils. 

It seems that liming, and the thorough underdraining 
of such lands, which have come into vogue, have now 
rendered these methods of tillage nearly or quite obsolete. 

TEXTURE OF SOILS INFLUENCED BY FERTILIZERS. 

There appears to be a large number of substances, and 
among them many of the chemical fertilizers, which have 
an appreciable influence in altering the texture of the 
soil, making it more or less open and friable. Among 
those which have the power of flocculating colloidal clay, 
lime has been most generally recognized, and it appears 
that this may be applied to the soil either as the oxide, 
hydrate, or carbonate, with the same ultimate effect, 
though perhaps with varying rates of action. We 
have already referred to Hilgard's and Schlosing's 
observations regarding this action of lime. 

More recently K. Sachsse and A. Becker have experi- 
mented with lime-water, gypsum, sulfate of magnesia, 
sulfate of ammonia, chlorides of potassium, sodium, 
and ammonium, and carbonic, hydrochloric, nitric, sul- 
furic, and silicic acids, as regards their power to bring 



286 The Soil. 

about a compounding of minute silt particles into clus- 
ters constituting grains of larger size. Working with a 
nearly pure kaolin, consisting of particles so small that 
only .5 per cent of them were as coarse as .0004 of an 
inch, they found one part of lime would flocculate 20.7 
parts of kaolin which had remained suspended in 27.777 
parts of water. A similar effect was observed upon a 
heavy clay loam, but not upon a humus alluvial loam. 
On examining the sizes of the particles, after flocculation 
had taken place, it was found that in the case of the 
kaolin and clay loam, the diameters of very many of 
them had materially increased, but that in the case of 
the alluvial soil no appreciable change had occurred. 

Studying the effects of lime on the percolation of 
water through kaolin and the clay loam, the persons 
referred to above found that while no water would pass 
through the untreated clay loam, yet when 61.2 cc. of 
water were poured over the tube treated with lime, it 
reached the bottom of the column in 1 hour and 10 min- 
utes, and 22.5 cc. drained through. In the case of the 
kaolin, of the 40 cc. added, 19 drained from the limed 
tube, while only a few drops percolated from the one 
untreated, and in that the kaolin swelled so much as to 
finally burst the tube. 

Carbonic acid flocculated the kaolin readily, and so did 
the hydrochloric, nitric, and sulfuric acids. While land 
plaster and the sulfates of magnesia and of ammonia 
were found to have the same power to some extent, their 
influence was not marked. Common salt and the chlo- 
rides of potash and ammonia also flocculated the clay 
and the kaolin, but the nitrate of soda had the opposite 
effect. 

If it is true that nitrate of soda has a tendency to 



Texture of Soils Influenced by Fertilizers. 287 

destroy the flocculation of clay soils and render them 
closer in texture, it would follow that, when supplies of 
nitrogen need to be added to these soils, they should be 
given in some other form than the Chile saltpetre. 

Either directly or indirectly, fertilizers exert an influ- 
ence upon the relation of water to the soil, as, indeed, 
has been implied in what has been said regarding their 
power to make the texture of the soil finer or coarser. 
If, by making the soil coarser grained, water percolates 
through it more readily, and its water-holding power is 
decreased, it should be expected that the capillary power 
will also be influenced; and observations have already 
been cited, showing that potassium nitrate increases the 
amount of water lifted by capillarity through a column 
of sand, while solutions of lime, land plaster, and salt 
decrease the amount, when compared with distilled 
water. Now, these effects may be brought about through 
changes in the texture of the soil or through a strength- 
ening or weakening of the surface tension. In the cases 
we have cited, on a former page, however, only the effect 
of the potassium nitrate is readily explained by either of 
these modes of action, taking Whitney's measurements of 
surface tension as a basis, because all of these salts are 
given as increasing it, while only one of them increased 
the rate of capillary rise through the sand; which cannot 
be assumed to have been materially altered by floccu- 
lation. 

When fertilizers are applied, the soil may react upon 
them either chemically or physically, and in such a 
manner as often to wholly prevent or greatly diminish 
their loss in drainage waters at times when percolation 
is taking place. Many observers have noted that, on 
filtering salt water through sand, the first which comes 



288 The Soil. 

through is nearly free from salt, bat when any soil 
becomes saturated, so to speak, with any particular 
fertilizer, then all excess may be leached away, and this 
fact has an important bearing on the application of ferti- 
lizers to lands, and shows that lighter dressings, often 
repeated, are likely to be less wasteful than heavier ones 
applied at longer intervals. This statement has even 
greater importance when applied to the organic ferti- 
lizers, like farmyard manure; for the richer a soil is in 
organic matter, the more rapidly will fermentation be set 
up in it under good tillage, and under these conditions 
nitrification is liable to be more rapid than is required 
to meet the demands of the crop on the ground. But if 
this is true, the soil becomes charged so that when per- 
colation takes place a large loss of nitrogen may occur. 
It is plain, therefore, that it is better to spread the 
manure over a larger area in the right amount than to 
concentrate it in heavy dressings on small areas. 



INFLUENCE OF FARMYARD MANURE ON SOIL 
MOISTURE. 

Farmyard manure has a marked effect upon the amount 
and disposition of soil moisture in cultivated fields. 
When coarse manure is plowed under, its first effect is 
to act as a mulch to the unstirred soil, by breaking the 
capillary connection between it and the surface layer. 
The tendency, therefore, is to cause the surface soil to 
become drier than it would otherwise have become in 
the same time, and frequently to an injurious extent, 
especially in times of spring droughts, before seeds have 
germinated or young plants have developed a root system 
reaching into the deeper soil. On such occasions as 



Farmyard Manure on Soil Moisture. 289 

these, the heavy roller is of service in making a better 
capillary connection with the unstirred subsoil. 

Farmyard manure has a general tendency to leave the 
upper three feet of soil more moist than it would be with- 
out it, and the drier the season and the more thorough 
the manuring, the more marked is its influence. In ex- 
periments to measure this influence under field conditions, 
the writer has found, as a mean of 3 years' work, that for 
manured fallow ground the surface foot contained 18.75 
tons more water per acre than adjacent and similar but 
unmanured land did, while the second foot contained 
9.28 tons and the third 6.38 tons more water, making a 
total difference in favor of the manured ground amount- 
ing to 34.41 tons per acre. The largest observed differ- 
ence was 72.04 tons in the dry season of 1891. Early in 
the spring, on ground manured the year before and 
fallow, there was an observed difference amounting to 
31.58 tons per acre. 

It is a fact long ago observed that increasing the 
organic matter in the soil increases its water-holding 
power, and this being true, it was to be expected that 
the surface foot would be more moist as a consequence 
of manuring, but by referring to the table on the next 
page, it will be seen that the influence of the manure is 
felt below the level to which it is applied. 

A part of the observed difference in the water content 
of manured and unmanured soils is to be explained by 
the fact that the rate of surface evaporation is dimin- 
ished by the dressing of dung. In the case of two 
cylinders 42 inches deep and holding nearly 600 pounds 
of soil, one manured and the other not, the writer found 
that the unmanured cylinder lost, in 105 days, at the rate 
of 108.5 tons more water per acre, a difference of about 



290 



The Soil. 



TABLE SHOWING EFFECT OF FARMYARD MANURE ON THE 
WATER CONTENT OF THE SOIL AT DIFFERENT DEPTHS 
BELOW THE SURFACE. 



Date. 



July 22,1891 
Sept. 12, 1891 
Apr. 11, 1892 
July 13, 1892 
Aug. 30, 1S92 
Aug. 12, 1893 
Sept. 9, 1893 



Mean . . . 

Difference . 

Tons per acre 



Surface 
Foot. 



Per cent. 



17.37 
13.75 



16.41 
12.76 



23.56 22.S6 



25. S9 
25.64 
19.07 
13.55 



19.SS 

1.09 

18.75 



24.36 
24.76 
17.91 
12.50 



1S.79 



2d Foot. 



Per cent. 



19.37 
16 41 
20.66 
24.01 
24.42 
17.35 
16.13 



19.79 

.46 

9.28 



17.63 
14.89 
20.55 
23.87 
24.34 
17.7S 
16.22 



19.33 



3d Foot. 



Per cent. 



17.03 
15.67 
18.26 
23.72 
24.21 
16.37 
16.90 



1S.S8 

.28 

6.38 



16.36 
14-49 
17.50 
23.29 
23.74 
17.88 
16.94 



IS. 60 



4th Foot. 



Per cent. 



12.00 
12.96 
16.50 
23.74 
21.69 
17.45 
16 71 



17.29 



12.7S 
11.59 
16.53 
23.32 
21.72 
17 99 
17.30 



17.32 
.03 
.69 



5th Foot, 



Per cent. 



14.69 
11.49 

16.SS 



14.35 



15.40 
10.96 
17.53 



14.63 

.28 

6.75 



6th Foot. 





H 




S 




P 


H 


fc 


« 


< 


P 


S 


< 


o 


a 


fe 



Per cent. 



18.01 
15.61 

19.72 



16.9S 



20.06 
15.99 
19.41 



17.13 

.15 

3.63 



1 ton per day. In another case wetting the surface of 
sand with water leached from manure reduced the rate 
of evaporation from the surface from 64.98 pounds per 
unit area to 32.72 pounds in the same time, under other- 
wise identical conditions. 

But the table shows that farmyard manure exerts an 
influence different from simply decreasing the surface 
evaporation ; for, while the upper three feet of the dunged 
land is more moist than that not so treated, the reverse 
is true when the next three feet are compared. Indeed, 
results analogous to wetting the surface soil and to 
firming it are observed. It appears as though the deeper 
soil water had been brought nearer to the surface, where 



Physical and Chemical Effects of Fallowing. 291 

it may become available for crop production, and in the 
writer's opinion this really does take place. 

On manured ground which is producing a crop, while 
a much larger yield of dry matter is produced per acre, 
the soil at the end of the growing season is found only 
a little drier, from which it follows, either that less 
water is required to produce a pound of dry matter in 
the rich soil, or else that the manure in some way makes 
more water available, and when the matter comes to be 
thoroughly understood, it is not improbable that both 
propositions will be found true. 

PHYSICAL AND CHEMICAL EFFECTS OF FALLOWING. 

That form of tillage known as fallowing exerts 
marked physical and chemical effects upon a soil, not 
felt, at least with like intensity, on lands heavily 
cropped. One of the most marked effects produced by 
fallowing is that exerted upon the water content of the 
soil. Not only is the fallow ground more moist during 
the fallowing period, as indeed should be expected, but 
the influence is felt the following spring, and even at the 
end of the harvest after the crop has been removed 
from the ground. 

The writer found, for example, in the spring succeed- 
ing a summer fallow, after all of the fall, winter, and 
spring rains, that the land which had been fallowed con- 
tained, in its upper four feet, 9.35 pounds to the square 
foot, or 203 tons per acre, more water than did that which 
had been cropped the season before. Nor was this all ; 
for at the end of the growing season and after large 
crops of oats and barley had been harvested from the 
land, there was still a difference in the water content of 



292 The Soil. 

the upper four feet amounting to 8.21 pounds on both the 
oat and barley ground, or 179 tons per acre. That the 
differences here recorded were not due to inherent dif- 
ferences in the soil, is proved by the water content of 
the same lands taken at three different times before the 
fallowing experiments began. The mean of these three 
determinations showed a difference of only .7 pounds in 
favor of the piece which was subsequently fallowed, as 
against 9.35 pounds in the spring and 8.21 pounds after 
the harvest succeeding the fallowing. It is plain, there- 
fore, that summer fallowing a piece of land exerts a 
strong influence over its relation to soil moisture, and 
one which is not outgrown for more than a year. 

Common experience, too, shows that the productiveness 
of the same lands is much increased, nor is it strange 
that this should be so. For when we call to mind the 
large stores of comparatively inert nitrogen which all 
good soils have been shown to possess, and then reflect 
upon the conditions which are most favorable to the 
nitrification of this humus, it must be very evident that 
in the warmer, more moist, and frequently stirred and 
aerated fallow field there must be a much larger conver- 
sion of inert nitrogen into active forms than could pos- 
sibly take place in the soil so thoroughly occupied by 
the roots of a crop ; that neither sufficient moisture nor 
other forms of food are available for the full and vigor- 
ous development of the microscopic soil life so indispen- 
sable to the processes here in question. When a soil is 
sapped to dryness and depleted of its soluble phosphates, 
lime and potash, the action of microscopic life in it 
must come nearly to a standstill and the development of 
fertility nearly cease. 

The Lois-Weedon system of tillage, which the Rev. 



Physical and Chemical Effects of Fallowing. 293 

Mr. Smith practiced in Northamptonshire for many 
years, was simply a judicious application of summer 
fallowing and a revival, in modern form, of the doctrine 
taught by Jethro Tull, between 1680 and 1740, that thor- 
ough and proper tillage might take the place of manure. 

Mr. Smith laid off his fields in lands 5 feet wide, 
and on these in successive years, by alternation, he grew 
wheat continuously, raising the yield per acre from 16 
bushels to 34, as an average of many years. In this 
rotation the fallow strips were frequently and deeply 
stirred, which favored the complete utilization of the 
native fertility of his soil and that left in the ground 
by the roots and stubble of the crop harvested. 

In adopting this system, Mr. Smith left a considerable 
portion of his land where nitrates could be developed 
in it under the best of conditions, and at the same time 
where the plants along the margins of the tilled lands 
could reach their roots out into the enriched soil and 
avail themselves of both its native moisture and its 
nitrates as they formed. 

The practice now in vogue in parts of Europe of grow- 
ing grain in drills far enough apart to permit of cultivat- 
ing the soil between the drills with horse cultivators, is 
carrying the idea of Tull and of Smith to the extreme 
limit, and is, of course, placing the growing of these 
crops on the same basis as that which we follow with so 
much success with corn, potatoes, and the like. 

The special advantage which these methods of summer 
fallowing, for such they in reality are, have over the old 
method of broad fields, is that the fertility developed 
may be utilized by the crop the same season, and thus the 
risk of losing a part of it through leaching by the winter 
and spring rains may be largely reduced. 



294 The Soil 

In very wet climates or more especially in those which, 
have heavy rainfall outside the growing season, so that 
excessive percolation and loss of plant food through 
drainage is large, summer fallowing in broad fields can- 
not be recommended. But in dry countries, where the 
loss of plant food through drainage channels is small, 
broad-field summer fallowing may in some cases prove 
decidedly advantageous, because, with the deficient rain- 
fall, there may not be moisture enough to mature a 
paying crop and at the same time to develop a suffi- 
cient store of plant food from the native fertility of 
the soil to meet the demands of the next season. At 
all events, the arguments urged against fallowing in 
countries like England do not apply to the semiarid 
districts of the world with equal force. 



INDEX. 



Abbot, Col., cut-offs in Mississippi 
River, 46. 

Actiniae, symbiotic life of, 129. 

Aeration of soil, influenced by 
drainage, 76. 

Aeration of soils, 239. 

Air and soil, 239. 

Air in soil retards percolation, 
173. 

Algre, symbiotic life of, 129. 

Aluminum, 79. 

Amazon, volume of discharge, 24. 

Ammonia, in air, 12 ; brought down 
by rain and snow, 119 ; absorbed 
by soil, 122; in air on Mont- 
souris, 123; decomposed by mi- 
cro-organisms, 131. 

Ammonium carbonate, absorbed 
by plants from the air, 122. 

Arendt, distribution of silica in 
plants, 97. 

Argon, amount of, in the atmos- 
phere, 11. 

Arid soils, texture, 29, 31; effect 
of lime in, 30, 94 ; amount of lime 
in, 30, 94 ; chemical composition 
of, 84, 85, 86, 87 ; compared with 
humid soils, 92. 

Ash ingredients, of plants, 101 ; 
relation between demand and 
supply, 113. 

Asphalt, origin of, 20. 

Atmosphere, its work, 9; pressure 
of, 9; relation of, to eating, 



drinking, and breathing, 10; 
depth of, 11; composition of, 11, 
23, 123; retains solar heat, 12; 
selective power of different con- 
stituents, 14; a distributing 
agent, 15; currents in, 23. 
Atwater, Prof., analysis of night- 
soil, 133. 



B. 



Bacteria, nitrifying, 125; observa- 
tions of Frank, Schlosing, Jr., 
Laurent, 129; producing ammo- 
nia, 131. 

Baker, J. O., quoted, 255. 

Barley, roots of, 208, 212. 

Barley, water used by, 155. 

Barometric pressure, oscillation 
due to changes in, 179. 

Beans, fixation of free nitrogen 
by, 124 ; water used by, 155. 

Becker, A., quoted, 285. 

Bisulfid of carbon, absorption of 
solar energy by, 8. 

Bitumen, origin of, 20. 

Blue grass, roots of, 212. 

Borax, 79. 

Boron, 79. 

Buckwheat, water used by, 156. 

Burning land, 283. 



C. 



Calcium, 80. 

Capillarity, 135, 138 ; measured in 



295 



f>96 



Index. 



horse power, 142; the work of 
sunshine in, 146. 

Capillary movement, 142; of soil 
water, 173 ; rate of, 174 ; in dry 
soil, 176; decreased hy plowing, 
177 ; influenced by dissolved 
salts, 177. 

Capillary tubes, height of water 
in, 140. 

Carbon, in soil, 77. 

Carbon dioxide, in air, 11 ; corrosive 
power of, 19; flocculation by, 
31, 76, 78. 

Catch crops, in relation to mois- 
ture, 190. 

Celtic land beds, 263. 

Chemical analyses of soils, 84, 85, 
86, 87 ; interpretation of, 89. 

Chile saltpetre, 81. 

Chlorine, 78, functions, 99; in 
rain water, 121. 

Chlorophyll, importance of iron, 98. 

Clay, in soil, 28; flocculated by 
lime, 30; colloid, 30; flocculated 
by carbon dioxide, 31 ; influence 
of drainage on texture of, 76; 
alumina in, 79 ; influence on per- 
colation, 172. 

Clayey soil, compared with sandy 
soil, 90 ; yields water to plants 
with difficulty, 161 ; contamina- 
tion of well water in, 169. 

Clover, ash ingredients, 102; in- 
creases soil nitrogen, 118, 124; 
water used by, 155. 

Clover, roots of, 208, 212. 

Coal, formed by life, 20. 

Cold waves, relation to storms, 14. 

Colloids, movements of, 153. 

Color of soil, and warmth, 230. 

Color waves, 7. 

Conservation of energy, 21. 

Conservation of moisture, 184. 

Corn, amount of water used by, 
155. 

Corn, roots of, 208, 209. 

Craigentinny meadows, 269. 



Crocker, amount of nitrogen in 

cultivated soil, 107. 
Cultivating to conserve moisture, 

192. 



D. 



Darwin, G. H., tidal friction, 17. 

Darwin, Charles, action of earth- 
worms, 62. 

Denitrification, 130, 132, 133. 

De Vries, observations on osmotic 
pressure, 148. 

Diffusion, 147. 

Drainage, 253. 

Drainage, influence of, on soil tex- 
ture, 76. 

Drains, movements of water in, 
due to soil air, 179. 

Dry-earth closets, 133. 

Dust, retards radiation, 14. 

E. 

Early seeding, 190. 

Earth, cooled by water, 16. 

Earthworms, 61. 

Eel grass, 67. 

Electricity, production of nitrous 
and nitric acids by, 123. 

Elliott, C. G., quoted, 264, 265. 

Erosion, by rains, 50 ; by glaciers, 
55, 58. 

Ether waves, velocity of , 6 ; complex 
character of, 7 ; absorbed by bi- 
sulfid of carbon and alum water, 
8 ; absorbed by water, 8. 

Evaporation and soil temperature, 
225. 

Evaporation, caused by sunshine, 
4, 145; nature of, 143; unneces- 
sary amount from plants, 156; 
retarded by deposit of salts on 
soil, 175. 

Evolution, organic, 31; relation of 
soil to, 31; of true roots, 35; of 
woody fibre, 36; of forest trees, 
36. 



Index. 



297 



F. 



Fallowing, effects of, 291. 

Fall plowing, 187. 

Farm drainage, 253. 

Farming, need for improved meth- 
ods, 3. 

Farmyard manure and soil mois- 
ture, 288. 

Fertilizers and soil texture, 285. 

Fertilizers, effects of, 276. 

Fertilizers, experiments of Sir J. 
B. Lawes, 105. 

Flocculation, by lime, 30; by car- 
bon dioxide, 76. 

Fluorine, 79. 

Forced meadows, 269. 

Frank, nitrifying bacteria, 129. 

Free nitrogen-fixing germs, 124. 



G. 



Gases, precipitation of minerals 
by, 20; origin of natural, 20. 

Glaciers, origin of, 54 ; in soil for- 
mation, 55 ; extent of action, 5(5 ; 
mode of action, 58; moraines of, 
60; magnitude of work, 61. 

Glauconite, 80. 

Granite, water absorbed by, 39. 

Greensand, 80. 

Gypsum, 78. 



H. 



Hanksbee, early studies of capil- 
larity, 136. 

Harrowing, to conserve moisture, 
192. 

Heat, absorption and radiation of, 
3; causing air currents, 4; part 
played in solution, 144. 

Hellriegel, fixation of free nitro- 
gen, 124; fixation of nitrogen by 
lupines, 126 ; water used by 
plants, 135 ; best amount of soil 
moisture, 161. 



Hiawatha, quoted, 211. 

Hilgard, E. W., effect of lime on 
clay, 30 ; lime in arid soils, 30, 
94 ; mechanical analyses of soils 
by, 70 ; composition of humus, 96. 

Hilgard, quoted, 285. 

Horse power, measure of solar 
energy expressed in, 6. 

Humid soils, 64; texture of, 29, 31 ; 
formation of, 64 ; in lakes, 66 ; by 
rivers, 65; chemical composition 
of, 84, 85, 86, 87 ; compared with 
arid soil, 92. 

Humus, 94 ; relation to fertility, 94 ; 
origin, 95; richer in nitrogen in 
arid regions, 96; Hilgard and 
Jaffa on composition, 96. 

Hydrogen, 78. 

Hygroscopic moisture, 252. 

I. 

Iceland moss, 34. 

Illinois, drainage in, 254. 

Iron, 81; importance in plant life, 

98. 
Irrigation, 268. 

J. 

Jaffa, composition of humus, 96. 

K. 

Kainite, 81. 
Kaolin, potash in, 81. 
Kelvin, Lord, 6. 

Kosswitsch, nitrifying bacteria, 
129. 



Lakes, overgrowing, 6(] ; formation 
of swamp soils in, 66 ; oscillations 
of, 179. 

Land plaster, 78 ; decreases capil- 
lary movement, 177. 



298 



Index. 



Langley, Professor, observations 
on atmospheric absorption, 13. 

Lathyrus sylvestris, roots of, 212. 

Laurent, nitrifying bacteria, 129. 

Lawes, Sir J. B., experiments on 
the influence of fertilizers, 105; 
nitrification of soils, 109. 

Leguminous plants, fixation of 
free nitrogen by, 124. 

Leonardo da Vinci, phenomena of 
capillarity, 136. 

Level culture and moisture, 202. 

Lichens, 34; examples of symbiosis, 
128, 130. 

Life, relation of water to, 18; its 
work in rock and soil building, 
18, 20; microscopic forms in soil, 
19; formation of coal, peat, etc., 
20 ; accumulation of phosphorus 
by, 79 ; symbiotic, 128 ; processes 
producing nitric acid, 131. 

Lime, effect on soil texture, 30; 
flocculation by, 30 ; in arid soils, 
94 ; amount in soil, 102; decreases 
capillary movement, 177. 

Limestones, formed by life, 20; 
composition, 80. 

Loess, 69 ; texture of, 75 ; chemical 
composition, 84, 85, 86, 87. 

Lois-Weedon system, 292. 

Lupines, fixation of free nitrogen 
by, 124 ; experiments by Hellrie- 
gel, 126. 

M. 

Madison River, shiftings of its 

course, 48. 
Magnesia, amount in soil, 102. 
Magnesium, 80. 
Maize, roots of, 208, 209. 
Maize, water used by, 24, 155. 
Manganese, 81; brown oxide of, 

93. 
Manitoba, amount of nitrogen in 

soils, 108. 
Manna, 34. 



Manure and moisture, 288. 

Marshall, quoted, 263. 

McGee, W. J., Mississippi bad 
lands, 50. 

Mechanical analysis of soil, 71, 90. 

Microscopic life in soil, 19, 20, 37 ; 
in fixation of nitrogen, 124; in 
the production of nitrous and 
nitric acids, 131; in denitrifica- 
tion, 132 ; deoxidation by, 132. 

Mississippi, bad lands, 50 ; soils, 70. 

Mississippi River, materials borne 
in solution, 17, 25 ; volume of dis- 
charge, 24; solids moved by, 25, 
48; bends in, 46; ox-bones, 46. 

Moisture and manure, 288. 

Moisture, conservation of, 184. 

Moisture, in air retards radiation, 
14. 

Montsouris, analysis of air on, 123. 

Moraines, 60. 

Moss, Iceland, 34; Reindeer, 34; 
Tripe de Roche, 34; sphagnum, 

m. 

Mother of petre, 241. 
Mulches, to conserve moisture, 194. 
Miintz, deoxidation in water- 
logged soils, 132. 
Myremill farm, 270. 

N. 

Nerust, W., nature of solution, 
145. 

Night soils, denitrification of, 133. 

Nitrates, deoxidation of, in soils, 
115 ; effects of percolation on 
distribution, 117 ; destruction of, 
131, 132 ; movement of, in plants, 
150. 

Nitre farming, 241. 

Nitric acid, 79; constituent of the 
atmosphere, 12; corrosive power 
of, 19; amount in soil, 114; in 
rain and snow, 119 ; produced by 
electricity, 123; life processes 
producing, 131. 



Index. 



299 



Nitrification, 130. 

Nitrogen, 11, 79; amount in the 
soil, 107; in soils of Manitoba, 
108; importance of, in plant 
growth, 111 ; relation between 
demand and supply, 113; forms 
of, in the soil, 114; stored as hu- 
mus, 115 ; distribution in the soil, 
115; sources of, in soil, 117; in 
soil increased by clover, 118; 
brought down by rain and snow, 
119; fixed by microscopic life, 
124; fixation by lupines, 127; 
Wagner's experiments, 127, 129; 
loss of, in night soils, 133. 

Nitrous acid, produced by elec- 
tricity, 123 ; produced by nitrous 
ferment, 131. 

Nitrous ferment, 131. 

Nollet, Abbe, early observation on 
osmosis, 148. 

O. 

Oak, roots of, 214. 

Oats, amount of water used by, 
155. 

Oats, roots of, 208, 212. 

Ocean, mean depth of, 16. 

Ochre, red and yellow, 81. 

Oil, origin of mineral, 20. 

Organic matter, deoxidation of, in 
soil, 115. 

Osmosis, 147; experiments in, 148. 

Ostwald, magnitude of surface ten- 
sion, 138. 

Outlets of drains, 266. 

Oxygen, 11; in soil, 77. 

Ozone, 12 ; action in producing ni- 
trous and nitric acids, 123. 

P. 

Paring land, 283. 

Peas, fixation of free nitrogen by, 

124, 126, 128; amount of water 

used by, 155. 
Pelouze, influence of size of grains 

on rate of solution, 74. 



Percolation, effect on distribution 
of nitrates, 117; rate of, from 
sand, 158, 171; of water into 
wells, 167; direction of, 170; 
rate of, through different soils, 
171 ; observations by Wollny, 
172; retarded by air in soil, 173; 
effected by barometric changes, 
179. 

Peroxide of hydrogen, action in the 
production of nitrous and nitric 
acids, 123. 

Pfeffer, W., observations on osmo- 
tic pressure, 148. 

Phosphoric acid, amount of, in 
manure, 74 ; amount in soil, 102. 

Phosphorus, 78 ; importance in 
plant life, 110. 

Physical effects of tillage, 276. 

Plants, relation to soil formation 
and soil destruction, 19; rela- 
tion to types of soil, 100; ash 
ingredients, 101 ; circulation in, 
149; movement of nitrates in, 
150; movements of starch, gum, 
and fats, 151; selective power 
in, 152; amount of water used 
by, 155; unnecessary evapora- 
tion from, 156. 

Plant feeding, process of, 149. 

Plant growth, part played by sun- 
shine in, 5 ; importance of nitro- 
gen, 110; amount of nitrogen 
demanded, 113. 

Plowing decreases the rate of 
capillary movement, 177. 

Plowing to save moisture, 187. 

Potash, amount of, in manure, 74 ; 
distribution, 80; amount in soil, 
102. 

Potassium, 80. 

Potassium carbonate, effect on 
capillary movement, 178. 

Potassium nitrate increases cap- 
illary movement, 177. 

Potatoes, amount of water used by, 
155. 



BOO 



Index. 



Precipitation, nature of, 4. 

Pressure of atmosphere, 9; meas- 
ure of, 9 ; relation of, to breath- 
ing, eating, and drinking, 10; 
variations of, the cause of winds, 
10 ; variations with light, 11. 

Q. 

Quartz, abundance of, in soil, 77. 
Quincke, surface tension, 139. 



K. 



Radiolaria, symbiotic life of, 129. 

Rainfall, insufficiency of, 25, 156. 

Rains, action in soil formation, 50; 
erosion by, in Mississippi, 50; 
ammonia and nitric acid brought 
down by, 119; composition of, 
120. 

Rains and soil warmth, 233. 

Rains for irrigating, 274. 

Ramsey, Prof., 11. 

Read, T. M., rock dissolved by 
water, 19. 

Reighley, Lord, 11. 

Richthofen, formation of loess, 
09. 

Rivers, action in soil formation, 
46, 48; in formation of swamp 
soils, 65; oscillations in, 179. 

Rock, thickness formed by water, 
17 ; structure of, in soil forma- 
tion, 38; fissures in soil forma- 
tion, 42; fractured by roots, 42. 

Rogers, the Messrs., experiments 
on the rate of solution, 74. 

Rolling, and soil temperature, 235. 

Rolling, effect on moisture, 200. 

Root hairs, part played in solution, 
146; osmotic movement in, 150. 

Roots, distribution of, 207. 

Roots, evolution of, 35 ; rocks frac- 
tured by, 42, 43; extent of con- 
tact with soil, 75; development 
in light soil, 99. 



Roots in drains, 266. 

Root surface, 207. 

Rotation of solid land, 26 ; of allu- 
vial soils, 48. 

Rothamsted, distribution of nitro- 
gen in soils, 115. 

Rye, amount of water used by ? 
155. 



S. 



Sachs, observations on function of 
iron, 98. 

Sachsse, quoted, 285. 

Salt, in rainwater, 121; decreases 
capillary movement, 177. 

Sand, water retained by, 157. 

Sandy soil, compared with clay 
soil, 90 ; size of grains, 100 ; water 
capacity influenced by distance 
to water table, 160; yields water 
to plants readily, 161. 

Schlosing, per cent of clay in soil, 
28; flocculation by carbon di- 
oxide, 31 ; absorption of ammo- 
nia by soil, 122; denitrification, 
132. 

Schlosing, quoted, 285. 

Seeding, early, 190. 

Seeds, ash ingredients of, 80. 

Shaler, formation of salt marshes, 
67. 

Shaler, quoted, 253. 

Shrinking of soils, 249. 

Silica, abundance of, in soils, 77 ; 
soluble, 84, 93, 102 ; functions, 97 ; 
distribution in oat plant, 97. 

Slope of land, and warmth, 228. 

Smith, Dr. Angus, composition of 
rain water, 120 ; denitrification in 
sewerage, 132. 

Smith, Rev., quoted, 292. 

Snow, ammonia and nitric acid 
brought down by, 119. 

Soap bubbles, illustrating surface 
tension, 136. 

Soda, amount in soil, 102. 



Index. 



301 



podium, 78, 81 ; chloride decreases 
capillary movement, 177. 

Soil, nature of, 27; clay in, 28; 
comparison of subsoil with, 29; 
texture of arid and humid, 29; 
a storehouse of water, 37 ; micro- 
scopic life in, 19, 37; formation 
by running water, 45, 46 ; over- 
placement of, 53 ; of glacial ori- 
gin, 55, 56; prairie, relation to 
glacial action, 60; swamp or 
humus, 64 ; formation by winds 
68; loess, 69; texture of, 70 
mechanical analyses of, 71 ; ex 
tent of contact of roots with, 75 
chemical constituents, 76 ; sandy 
description of, 82; clayey, 83 
chemical composition of, 84, 85 
86, 87 ; kinds, 99 ; warm and cold 
99 ; amount of nitrogen in, 107 
distribution of nitrogen in, 115 
absorbs ammonia from the air 
122; capillary rise of water in 
139, 141 ; water capacity, 157 
159; rate of capillary rise in 
174, 176. 

Soil air, movements of soil water 
due to, 178; producing diurnal 
oscillations of soil water, 180. 

Soil grains, size of, 72 ; influence 
of size on water capacity, 72, 
157, 160; smallest not individu- 
ally invested by water films, 73; 
influence of size on rate of solu- 
tion, 72 ; compound structure of, 
75 ; in varieties of soil, 100 ; influ- 
ence of size on percolation, 
171. 

Soil moisture, part played in soil 
fertility, 154; best amount of, 
161 ; conservation of, 177. 

Soil temperature, 218. 

Soil texture, 70; influence of, on 
water capacity, 72 ; influence of, 
on food supply, 74 ; influenced by 
drainage, 76; influence of, on 
capillary movement, 176, 177. 



Soil water, movements of, 170, 173 ; 
movements due to soil air, 178 ; 
diurnal oscillations of, 180. 

Solution, 142 ; Pelouze and Rogers, 
experiments on rate of, 74 ; influ- 
ence of size of soil particles on 
rate of, 74 ; nature of, 142 ; influ- 
ence of temperature on, 144; part 
played by root hairs in, 146. 

Sphagnum moss, 66. 

Springs, flow of, influenced by 
barometric changes, 180. 

Spring plowing, 188. 

Starch, movements of, in plants, 
151. 

Storer, amount of nitrogen in soil, 
107 ; dry-earth closets, 133. 

Storer, quoted, 269. 

Sub-irrigation, 260; natural, 171. 

Subsoil, 29; chemical composition, 
84, 85, 86, 87; compared with 
soil, 92. 

Sulfur in soil, 78, 97. 

Sulfuric acid, amount in soil, 102; 
in rain water, 121. 

Sun, work done by, 6. 

Sunshine and its work, 3; nature 
of, 3; causing evaporation, 4; 
stored in the soil, 5 ; part played 
in plant growth, 5; velocity of, 
6; measured in horse power, 6; 
absorbed by bisulfid of carbon, 
8 ; snow and ice opaque to dark 
rays of, 8; solution and move- 
ment of plant food, 144 ; in capil- 
larity, 146. 

Surface drainage, 262. 

Surface tension, 136; magnitude 
of, 138; distance over which it 
acts, 139; part played in solu- 
tion, 143; modified by dissolved 
salts, 177. 

Swamp soils, 64; formation by 
rivers, 65; in lakes, 66; by the 
sea, 66 ; by eel-grass, 67 ; chemi- 
cal composition, 84, 85, 86, 87. 

Symbiosis, 128, 134, 



302 



Index. 



Temperature of soils, 218. 

Temperature of the earth without 
an atmosphere, 13; changes of, 
in soil formation, 39; influence 
on solution, 144; influence on 
water capacity, 160; diurnal os- 
cillations of soil water due to 
changes of, 183. 

Texture of soil, 70; influenced by- 
drainage, 76. 

Texture of soils influenced by fer- 
tilizers, 285. 

Tidal friction, 17. 

Tillage and moisture, 192. 

Tillage, deep, and moisture, 202. 

Tillage, physical effects of, 276. 

Tilth, importance of, 277; to se- 
cure, 279. 

Timothy, roots of, 212. 

Translocation of moisture, 195. 

Tripe de Roche, 34. 

Tubercles on roots of leguminous 
plants, 124, 125. 

Tull, Jethro, 293. 

U. 

Underdraining, 257. 
Underdrawing and aeration, 248. 
Underdraining and temperature, 
225. 

V. 

Van't Hoff , nature of solution, 145. 
Velocity of ether waves, 6. 
Ventilation of soils, 239. 
Voeleker, composition of farmyard 
manure, 74. 



W. 



Wagner, P., fixation of nitrogen by 
peas, 127 ; importance of nitric 
nitrogen, 129. 



Waring, Col., dry-earth closets, 
133. 

Warington, nitrogen removed from 
soil by wheat, 107 ; amount of 
nitric acid in soil, 114; produc- 
tion of nitrous acid, 123 ; produc- 
tion of nitric acid, 123; denitrifi- 
cation in water-logged soils, 132. 

Warmth of soils, 220. 

Water in soils, 184. 

Water, opaque to dark rays, 8 ; 
and its work, 16; cooling the 
earth, 16; retards earth's rota- 
tion, 17; dissolving and trans- 
porting power, 17, 19 ; importance 
in life processes, 18 ; magnitude 
of movement of, 24 ; absorbed by 
rocks, 39 ; freezing of, in soil for- 
mation, 39 ; solvent action of, 39 ; 
running, in soil formation, 45; 
amount used by plants, 155 ; ca- 
pacity of soils for, 155 ; retained 
by sand, 157 ; capacity of field 
soils for, 159; yielded to plants 
by kinds of soil, 161 ; contamina- 
tion of, in wells, 167 ; percolation 
into wells, 168; rate of capillary 
rise in soil, 174, 176. 

Water capacity, influence of size of 
soil grains on, 72 ; of field soils, 
159. 

Water films, on soil grains, 72. 

Water table, 163; influence on 
water capacity of soils, 160 ; po- 
sition influences land values, 162; 
altitude of, 163; height variable, 
163 ; wells most affected by sea- 
sonal changes, 166. 

Waves, ether, 6; velocity of, 6; 
complex character of, 7; kinds 
of, 7 ; absorbed by water, 8. 

Weight of soils, 185. 

Wells, 162, 167 ; relation to water 
table, 163; conditions to be ob- 
served in digging, 166; most 
affected by seasonal changes of 
the water table, 166 ; depth below 



Index. 



303 



water table influences capacity, 

167; contamination of water in, 

167 ; movements of water in, due 

to soil air, 179. 
Wheat, amount of water used by, 

155. 
Wheat, roots of, 212. 
Whitney, mechanical analyses of 

soils, 91. 
Wiley, mechanical analyses of soils, 

90. 
Wilson, H. M., quoted, 273. 



Wilson, John, quoted, 270. 

Windmills for irrigating, 274. 

Winds and soil moisture, 204. 

Winds, systems of, 23 ; soils formed 
by, 68; caused by sunshine, 4; 
maintain uniform composition of 
air, 23. 

Wolff, ash ingredients of plants, 
101. 

Wollny, observations on percola- 
tion, 172. 



THE RURAL SCIENCE SERIES. 

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many plants are grown, directions for making potting-earth and of caring for plants, 
etc. ; a chapter on " Literature," giving classified lists of all the leading current 
books on American horticulture, and directories of officers of whom the bulletins of 
the various experiment stations maybe obtained; lists of self-fertile and self-sterile 
fruits; a full account of the methods of predicting frosts and of averting their injuries; 
a discussion of the aims and methods of phenology, or the record of climate in the 
blooming and leafing of trees; the rules of nomenclature adopted by botanists and by 
various horticultural societies; score-cards and scales of points for judging various 
fruits, vegetables, and flowers; a full statement of the metric system, and tables of 
foreign money. 



MACMILLAN & CO., 

66 FIFTH AVENUE, NEW YORK. 



